Pass betterproto option using custom_opt instead of environment variable

Author: boukeversteegh

README.md

@@ -360,13 +360,17 @@ $ pipenv run test
 Betterproto includes compiled versions for Google's well-known types at [betterproto/lib/google](betterproto/lib/google).
 Be sure to regenerate these files when modifying the plugin output format, and validate by running the tests.
 
-Normally, the plugin does not compile any references to `google.protobuf`, since they are pre-compiled. To force compilation of `google.protobuf`, set this environment variable: `BETTERPROTO_OPTS=INCLUDE_GOOGLE`. 
+Normally, the plugin does not compile any references to `google.protobuf`, since they are pre-compiled. To force compilation of `google.protobuf`, use the option `--custom_opt=INCLUDE_GOOGLE`. 
 
 Assuming your `google.protobuf` source files (included with all releases of `protoc`) are located in `/usr/local/include`, you can regenerate them as follows:
 
 ```sh
-export BETTERPROTO_OPTS=INCLUDE_GOOGLE
-protoc --plugin=protoc-gen-custom=betterproto/plugin.py --custom_out=betterproto/lib -I/usr/local/include/ /usr/local/include/google/protobuf/*.proto
+protoc \
+    --plugin=protoc-gen-custom=betterproto/plugin.py \
+    --custom_opt=INCLUDE_GOOGLE \
+    --custom_out=betterproto/lib \
+    -I /usr/local/include/ \
+    /usr/local/include/google/protobuf/*.proto
 ```
 
 

betterproto/plugin.py

@@ -120,8 +120,7 @@ def get_comment(proto_file, path: List[int], indent: int = 4) -> str:
 
 
 def generate_code(request, response):
-    plugin_options = os.environ.get("BETTERPROTO_OPTS")
-    plugin_options = plugin_options.split(" ") if plugin_options else []
+    plugin_options = request.parameter.split(",") if request.parameter else []
 
     env = jinja2.Environment(
         trim_blocks=True,