Merge branch 'minor_doc_updates' into 'master'

Minor doc updates

## What does this MR do?

Adds to and clarifies some documentation. Specifically, when using `gdb` to debug you need to detach and exit when done. Next, this clarifies the type of file locking that we require.

Thanks to @northrup for the details about mandatory vs. advisory file locking.

Note: These were two really small changes so I combined in to one merge request. However, I left the commits separate for clarity.

See merge request !4421