Document how to recompile proto files

Author: AdrienVannson

docs/development.md

@@ -0,0 +1,25 @@
+# Development
+
+## Recompiling the lib proto files
+
+After some updates in the compiler, it might be useful to recompile the standard Google proto files. As the proto files
+are distributed with `protoc`, their path might depend on your installation.
+
+```bash
+mkdir lib
+protoc \
+    --python_betterproto2_opt=INCLUDE_GOOGLE \
+    --python_betterproto2_out=lib \
+    -I /usr/include/ \
+    /usr/include/google/protobuf/*.proto
+```
+
+The generated files should be distributed in the `betterproto2` package.
+
+!!! warning
+    These proto files are written with the `proto2` syntax, which is not supported by betterproto. For the compiler to
+    work, you need to manually patch the generated file to mark the field `oneof_index` in `Field` and
+    `FieldDescriptorProto` optional.
+
+In the compiler, you also need to compile the [plugin.proto](https://github.com/protocolbuffers/protobuf/blob/main/src/google/protobuf/compiler/plugin.proto)
+file in `src/betterproto2_compiler/lib/google.protobug/compiler/__init__.py`.

mkdocs.yml

@@ -14,6 +14,7 @@ nav:
   - Betterproto2 compiler:
      - index.md
      - Getting started: getting-started.md
+     - Development: development.md
 
 plugins:
 - mkdocstrings