Python code-gen; doc about setting

The recently added Python code-generation handling
system now has a setting to control the additional
query. This PR contains a documentation tweak to
point this out.

docs/python/code-generators.md

@@ -16,5 +16,10 @@ See the Python example [simple_code_generator](/examples/python/simple_code_gene
 
 The Bazel Intelli-J plugin is able to work with generated Python code in this situation. You need to ensure that your code generator has no `srcs` attribute and that it has a tag `intellij-py-code-generator`. This tag signals to the plugin that the Rule's output is generated code.
 
+During a full sync, the plugin will need to execute an additional Bazel `query` in order to locate rules with the tag. This is an unavoidable overhead of this approach and so that the cost of this is only borne by projects that require it, there is a setting to enable it. You will find the file to add the setting in the `.ijwb` directory in your project files. Inside this directory is a file with extension `.bazelproject`; add the following line into this file.
+
+```
+enable_python_codegen_support: true
+```