protoc: add page for Google Protobuf (#1698)

pages/common/protoc.md

@@ -0,0 +1,15 @@
+# protoc
+
+> Parse Google Protobuf `.proto` files and generate output in the specified language.
+
+- Generate Python code from a `.proto` file:
+
+`protoc --python_out={{path/to/output_directory}} {{input_file.proto}}`
+
+- Generate Java code from a `.proto` file that imports other `.proto` files:
+
+`protoc --java_out={{path/to/output_directory}} --proto_path={{path/to/import_search_path}} {{input_file.proto}}`
+
+- Generate code for multiple languages:
+
+`protoc --csharp_out={{path/to/c#_output_directory}} --js_out={{path/to/js_output_directory}} {{input_file.proto}}`