Reorganized README.md

[Ronqn]

Fixes #636

Created new files called NOTES.md, FILES.md, RELEASES.md and moved them alongside CONTRIBUTING.md and SECURITY.md in a new folder called "docs".

Updated the README.md to reflect these changes.

[stleary]

What problem does this code solve?
Updating the readme and other documentation, which was getting a bit unwieldy.

Risks
Low

Changes to the API?
N/A

Will this require a new release?
No

Should the documentation be updated?
This is the documentation

Does it break the unit tests?
N/A

Was any code refactored in this commit?
N/A

Review status
ACCEPTED

[stleary]

Skipping the 3-day comment window, since this is a doc change.