[Issue 5775][Doc] Description of broker-tool added (apache#6011)

* bugfix#4981byBGRichi

* Bugfix#5768

* Revert "Bugfix#5768"

This reverts commit e6e45cd.

* Revert "bugfix#4981byBGRichi"

This reverts commit 4f1c371.

* bugfix#5775: broker-tool section added

site2/docs/reference-cli-tools.md

@@ -13,6 +13,7 @@ All Pulsar command-line tools can be run from the `bin` directory of your [insta
 * [`pulsar-daemon`](#pulsar-daemon)
 * [`pulsar-perf`](#pulsar-perf)
 * [`bookkeeper`](#bookkeeper)
+* [`broker-tool`](#broker-tool)
 
 > ### Getting help
 > You can get help for any CLI tool, command, or subcommand using the `--help` flag, or `-h` for short. Here's an example:
@@ -624,7 +625,7 @@ The table below lists the environment variables that you can use to configure th
 |BOOKIE_LOG_CONF|Log4j configuration file|conf/log4j2.yaml|
 |BOOKIE_CONF|BookKeeper configuration file|conf/bk_server.conf|
 |BOOKIE_EXTRA_OPTS|Extra options to be passed to the JVM||
-|BOOKIE_EXTRA_CLASSPATH|Extra paths for BookKeeper's classpath||  
+|BOOKIE_EXTRA_CLASSPATH|Extra paths for BookKeeper's classpath||
 |ENTRY_FORMATTER_CLASS|The Java class used to format entries||
 |BOOKIE_PID_DIR|Folder where the BookKeeper server PID file should be stored||
 |BOOKIE_STOP_TIMEOUT|Wait time before forcefully killing the Bookie server instance if attempts to stop it are not successful||
@@ -696,3 +697,34 @@ Example
 $ bookkeeper shell bookiesanity
 ```
 
+## `broker-tool`
+
+The `broker- tool` is used for operations on a specific broker.
+
+Usage
+```bash
+$ broker-tool command
+```
+Commands
+* `load-report`
+* `help`
+
+Example
+Two ways to get more information about a command as below:
+
+```bash
+$ broker-tool help command
+$ broker-tool command --help
+```
+
+### `load-report`
+
+Collect the load report of a specific broker. 
+The command is run on a broker, and used for troubleshooting why broker can’t collect right load report.
+
+Options
+|Flag|Description|Default|
+|---|---|---|
+|`-i`, `--interval`| Interval to collect load report, in milliseconds ||
+|`-h`, `--help`| Display help information ||
+