chore: custom networks dev docs (#11943)

Author: grandizzy

crates/evm/networks/README.md

@@ -13,7 +13,7 @@ To add configuration support for a custom network (e.g. `my_network`), add a new
     pub my_network: bool,
 ```
 
-This automatically enables::
+This automatically enables:
 - `my_network = true` in foundry.toml
 - `--my-network` anvil CLI flag
 ```

docs/dev/README.md

@@ -51,6 +51,7 @@ $ make pr
 - [Cheatcodes](./cheatcodes.md)
 - [Debugging](./debugging.md)
 - [Scripting](./scripting.md)
+- [Custom Network Features](./networks.md)
 
 _Note: This is incomplete and possibly outdated_
 

docs/dev/networks.md

@@ -0,0 +1,6 @@
+# Custom Network Features
+
+Foundry's `anvil`, `forge` and `cast` tools can be customized with specific network features (currently with custom 
+precompiles, with planned support for custom transaction types).
+
+For supporting custom features of a network, please check out documentation and examples within [`evm-networks`](../../crates/evm/networks) crate.