Add Documentation for adding scratch path feature to python plugins

[nhlien93]

Currently the docs don’t mention how to use the scratch path, have example code snippets for how the scratch path can be used, or suggest what should/should not go in the scratch path (for example, logging statements should use the Python PlatformHandler logger, instead of putting logs into the scratch path). Documentation changes would require a couple small tasks: adding code snippets and verifying that they are correct, adding explanations, and informing plugin users that plugins can write anything it wants to in the scratch path.