Fleshing out the crate disclaimer a bit further

guides/diesel-setup.md

@@ -1,6 +1,10 @@
 # Diesel setup
 
-**Disclaimer:** the barrel crate is still in an early state of development and should not be considered "stable". Use at your own risk!
+
+### Disclaimer
+> The barrel crate is still in an early state of development and should not be considered "stable". 
+>
+> Old migrations might break because the API was changed. Features might be removed or replaced! **Before 1.0 this crate is not stable and should __not__ be used in production** – just wanted to make that loud and clear :)
 
 Using rust migrations (via `barrel`) with `diesel` is really simple. First, you need to add the `rust-migrations` to the features list for your `diesel` dependency. Note that currently `barrel` only supports postgres databases.
 
@@ -23,4 +27,16 @@ From this point using `diesel` is very similar to how you normally use it. The o
 ~ diesel migration generate <name> --type="rust"
 ~ diesel migration run
   ...
-```
+```
+
+A migration file generated by diesel will look as follows
+
+```rust
+/// Handle up migrations
+fn up(migr: &mut Migration) {}
+
+/// Handle down migrations
+fn down(migr: &mut Migration) {}
+```
+
+The object provided as a function parameter is a mutable `Migration` object which you can operate on. Please refer to  [the docs](https://docs.rs/barrel/0.2.0/barrel/migration/struct.Migration.html) for API specifics.