Use github actions to pull tool documentation into wiki

[simoninns]

Right now the documentation is a bit 'remote' from the code - keeping the documentation in the main repo (for things like ld-decode.py and the tool-chain) would allow PR reviewers to ensure documentation and code are updated at the same time.

I'm thinking perhaps there can be a "standard" - each tool/etc must provide a docs/ directory that contains userguide.md and any associated pngs etc. Readme.md could also be part of this too - but we'd need to think about the way to gets used in the wiki.

Then we set up some github actions to:

1. Clone the .wiki.git repo
2. Copy the file over
3. Commit and push automatically

Clearly the wiki structure would have to be modified a bit to do this, but it could help to a) lower the work of wiki maintenance and b) keep everything up to date.

Downside is, tool documentation has to be done via PRs, but that's a small price imho.

[simoninns]

This is now up and running (but is currently under test):

https://github.com/happycube/ld-decode-docs

with the resulting documentation here:

https://happycube.github.io/ld-decode-docs/

Feel free to try it out.