feature: doc/opencode.txt

[justinmk]

Did you check the docs?

• I have read all the docs

Is your feature request related to a problem? Please describe.

Missing doc/opencode.txt file so I can't use :help in Nvim.

Describe the solution you'd like

Provide doc/opencode.txt as the main source of documentation.

Describe alternatives you've considered

Reading the readme, which (currently) is not supported by :help.

Additional context

No response

[nickjvandyke]

Thanks for the suggestion, this is definitely on my list as the plugin stabilizes 🙂