fix some docs and add new content (apache#3369)

docs/content/development/extensions-contrib/orc.md

@@ -12,11 +12,11 @@ This extension enables Druid to ingest and understand the Apache Orc data format
 
 This is for batch ingestion using the HadoopDruidIndexer. The inputFormat of inputSpec in ioConfig must be set to `"org.apache.hadoop.hive.ql.io.orc.OrcNewInputFormat"`.
 
-Field     | Type        | Description                                                                            | Required
-----------|-------------|----------------------------------------------------------------------------------------|---------
-type      | String      | This should say `orc`                                                                  | yes
-parseSpec | JSON Object | Specifies the timestamp and dimensions of the data. Any parse spec that extends ParseSpec is possible but only their TimestampSpec and DimensionsSpec are used. | yes
-typeString| String      | String representation of Orc struct type info. If not specified, auto constructed from parseSpec but all metric columns are dropped | no
+|Field     | Type        | Description                                                                            | Required|
+|----------|-------------|----------------------------------------------------------------------------------------|---------|
+|type      | String      | This should say `orc`                                                                  | yes|
+|parseSpec | JSON Object | Specifies the timestamp and dimensions of the data. Any parse spec that extends ParseSpec is possible but only their TimestampSpec and DimensionsSpec are used. | yes|
+|typeString| String      | String representation of Orc struct type info. If not specified, auto constructed from parseSpec but all metric columns are dropped | no|
 
 For example of `typeString`, string column col1 and array of string column col2 is represented by `"struct<col1:string,col2:array<string>>"`.
 

docs/content/development/extensions-contrib/parquet.md

@@ -12,10 +12,10 @@ This extension enables Druid to ingest and understand the Apache Parquet data fo
 
 This is for batch ingestion using the HadoopDruidIndexer. The inputFormat of inputSpec in ioConfig must be set to `"io.druid.data.input.parquet.DruidParquetInputFormat"`. Make sure also to include "io.druid.extensions:druid-avro-extensions" as an extension.
 
-Field     | Type        | Description                                                                            | Required
-----------|-------------|----------------------------------------------------------------------------------------|---------
-type      | String      | This should say `parquet`                                                              | yes
-parseSpec | JSON Object | Specifies the timestamp and dimensions of the data. Should be a timeAndDims parseSpec. | yes
+|Field     | Type        | Description                                                                            | Required|
+|----------|-------------|----------------------------------------------------------------------------------------|---------|
+|type      | String      | This should say `parquet`                                                              | yes|
+|parseSpec | JSON Object | Specifies the timestamp and dimensions of the data. Should be a timeAndDims parseSpec. | yes|
 
 For example:
 

docs/content/development/extensions.md

@@ -36,8 +36,11 @@ Core extensions are maintained by Druid committers.
 
 # Community Extensions
 
-A number of community members have contributed their own extensions to Druid that are not packaged with the default Druid tarball. 
-Community extensions are not maintained by Druid committers, although we accept patches from community members using these extensions. 
+<div class="note caution">
+Community extensions are not maintained by Druid committers, although we accept patches from community members using these extensions. They may not have been as extensively tested as the core extensions. 
+</div>
+
+A number of community members have contributed their own extensions to Druid that are not packaged with the default Druid tarball.  
 If you'd like to take on maintenance for a community extension, please post on [druid-development group](https://groups.google.com/forum/#!forum/druid-development) to let us know!
 
 All of these community extensions can be downloaded using *pull-deps* with the coordinate io.druid.extensions.contrib:EXTENSION_NAME:LATEST_DRUID_STABLE_VERSION.

docs/content/operations/rule-configuration.md

@@ -128,5 +128,10 @@ The interval of a segment will be compared against the specified period. The per
 
 # Permanently Deleting Data
 
- Druid can fully drop data from the cluster, wipe the metadata store entry, and remove the data from deep storage for any segments that are 
- marked as unused (segments dropped from the cluster via rules are always marked as unused). You can submit a [kill task](../ingestion/tasks.html) to the [indexing service](../design/indexing-service.html) to do this.
+Druid can fully drop data from the cluster, wipe the metadata store entry, and remove the data from deep storage for any segments that are 
+marked as unused (segments dropped from the cluster via rules are always marked as unused). You can submit a [kill task](../ingestion/tasks.html) to the [indexing service](../design/indexing-service.html) to do this.
+
+# Reloading Dropped Data
+
+Data that has been dropped from a Druid cluster cannot be reloaded using only rules. To reload dropped data in Druid, you must first set your retention period (i.e. changing the retention period from 1 month to 2 months), and 
+then enable the datasource in the Druid coordinator console, or through the Druid coordinator endpoints.