docs(website): more info on /contribute

[thehowl]

forgot these as part of #2742

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.43%. Comparing base (d5015ab) to head (8845726).
Report is 10 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2765      +/-   ##
==========================================
- Coverage   60.44%   60.43%   -0.01%     
==========================================
  Files         563      563              
  Lines       75149    75149              
==========================================
- Hits        45426    45420       -6     
- Misses      26335    26341       +6     
  Partials     3388     3388              

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
contribs/gnofaucet	15.31% <ø> (+0.85%)	⬆️
gno.land	67.21% <ø> (ø)
gnovm	64.46% <ø> (ø)
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	62.07% <ø> (+0.11%)	⬆️

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