Starting some doc revamping

This is an ongoing project to revamp the YTDL-Sub docs.
Starting point:

- Recreate docs folder/file structure
- Update root makefile to use new make docs command
- Move old docs into new docs folder structure (as a base)
- Separate out old docs into individual files to allow better navigation with the new theme

docs/source/guides/getting_started/initial_setup.rst

@@ -0,0 +1,5 @@
+Initial Setup
+=============
+If you haven't read it yet, it's highly recommended to go through our
+`walk-through guide <https://github.com/jmbannon/ytdl-sub/wiki/1.-Introduction>`_
+to get familiar with how ``ytdl-sub`` works.