docs: Expand feature flags docs in contributors' guide (meltano#6697)

* Clarify feature_flags usage and implementation in contribute docs

* Clarify feature flags usage and implementation

* Prettify

docs/src/_contribute/style.md

@@ -12,6 +12,7 @@ weight: 10
 Meltano uses the below tools to enforce consistent code style. Explore the [repo](https://github.com/meltano/meltano) to learn of the specific rules and settings of each.
 
 Python:
+
 - [isort](https://pycqa.github.io/isort/)
 - [Black](https://github.com/ambv/black)
 - [Flake8](https://flake8.pycqa.org/en/latest/)
@@ -24,6 +25,7 @@ and `wemake-python-styleguide` is a plugin for Flake8 that offers an extensive s
 [MyPy is currently not executed in CI](https://github.com/meltano/meltano/issues/6491). It currently raises many issues when run. We intend to address them over time.
 
 Javascript:
+
 - [ESLint](https://eslint.org/docs/rules/)
 - [ESLint Vue Plugin](https://github.com/vuejs/eslint-plugin-vue)
 - [Prettier](https://prettier.io/)
@@ -76,31 +78,42 @@ Object properties and methods are alphabetical where `Vuex` stores are the excep
 ### Feature Flags
 
 Sometimes it is useful to be able to make preview features available or allow deprecated features to be used for backwards compatibility.
+
 To accomplish this, Meltano implements feature flags.
-For new, deprecated, or experimental features, the relevant code path can be wrapped in a feature flag context.
 
-For example:
+For new, deprecated, or experimental features, the relevant code path can be wrapped in a feature flag context. The process for adding new feature flags is as follows:
+
+1. Determine a descriptive name for the feature flag and add it as a [`FeatureFlags` Enum value](https://github.com/meltano/meltano/blob/3237022624c9594852abe69acb4da3dbf1ce5c05/src/meltano/core/settings_service.py#L30)
+1. Wrap your code blocks in a `ProjectSettingsService.feature_flag()` context as demonstrated below.
+1. Add documentation about the new feature flag to the [Feature Flags section of the settings reference docs](/reference/settings#feature-flags)
+1. In any documentation about the feature, note that the feature is experimental and link to the [Feature Flags section of the settings reference docs](/reference/settings#feature-flags). This note should be something similar to:
+   > This feature is experimental and must be enabled using feature flags. See the docs here: ...
+1. Add your feature flag metadata to [settings.yml](https://github.com/meltano/meltano/blob/3237022624c9594852abe69acb4da3dbf1ce5c05/src/meltano/core/bundle/settings.yml#L189) so that it is recognized as a project-wide configuration setting.
+
 ```python
+# Example feature flag usage
+from meltano.core.project import Project
 from meltano.core.project_settings_service import ProjectSettingsService
-from meltano.core.settings_service import EXPERIMENTAL
+from meltano.core.settings_service import FeatureFlags
 
 class ExistingClass:
 
     def __init__(self):
         self.project = Project.find()
         self.settings_service = ProjectSettingsService(self.project)
 
-    # If this method is called elsewhere in the code and experimental features are
-    # not allowed, it will throw an error:
+    # If this method is called elsewhere in the code and the NEW_BEHAVIOR
+    # feature flag is not set to 'true' it will throw an error:
     def experimental_method(self):
-        with self.settings_service.feature_flag(EXPERIMENTAL):
-            print("Doing experimental behavior...")
+        with self.settings_service.feature_flag(FeatureFlags.NEW_BEHAVIOR):
+            print("Doing new behavior...")
 
     # If this method is called elsewhere, its behavior will vary based on whether
     # the feature flag is set in the project
     # The same pattern can be used to deprecate existing behavior
+    # Notice the "raise_error=False" in the feature_flag method call
     def existing_method_with_new_behavior(self):
-        with self.settings_service.feature_flag("new_behavior") as new_behavior:
+        with self.settings_service.feature_flag(FeatureFlags.NEW_BEHAVIOR, raise_error=False) as new_behavior:
             if new_behavior:
                 print("Doing the new behavior...")
             else: