MSA Pallet Docs

[wilwade]

Goal

The goal of this PR is to improve the documentation of the Pallets and make that documentation be able to be used on docs.frequency.xyz.

Part of https://github.com/frequency-chain/docs/issues/59

Discussion

• This is the first one, so it includes the needed documentation and templates as well.
• Please suggest additional content that would be useful as well
• Had a hard time getting it to look nice in both markdown and the rendered html.
• Disabling soft wrap will help it look better
• The idea was to keep rust specific things out of the readme and in the lib.rs

Testing

• make docs
• open target/doc/pallet_msa/index.html

Screenshots

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files	Coverage Δ
pallets/msa/src/lib.rs	87.90% <100.00%> (ø)

[jeanettedepatie]

In my view, the Extrinsics table is cut off on the bottom.