doc: Add contributing documentation

[lengrongfu]

Signed-off-by: lengrongfu [email protected]

Thank you for contributing to Harbor!

Comprehensive Summary of your change

This is based on the problems and summary I encountered in the process of modifying the project code for the first time, and added a basic newcomer development document. If there are any better operation steps, you can propose or improve it later. Thanks.

Issue being fixed

Fixes #(issue) https://github.com/goharbor/harbor/issues/17299

Please indicate you've done the following:

• [x] Well Written Title and Summary of the PR
• [x] Label the PR as needed. "release-note/docs"
• [x] Accepted the DCO. Commits without the DCO will delay acceptance

[codecov[bot]]

Codecov Report

Merging #17314 (8a980dc) into main (0fbff49) will decrease coverage by 0.09%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main   #17314      +/-   ##
==========================================
- Coverage   43.24%   43.14%   -0.10%     
==========================================
  Files         235      235              
  Lines       13183    13183              
  Branches     2677     2677              
==========================================
- Hits         5701     5688      -13     
- Misses       7166     7177      +11     
- Partials      316      318       +2     

Flag	Coverage Δ
unittests	43.14% <ø> (-0.10%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...es/vulnerability/vulnerability-config.component.ts	54.07% <0.00%> (-8.89%)	:arrow_down:
...ortal/src/app/shared/pipes/harbor-datetime.pipe.ts	32.00% <0.00%> (-4.00%)	:arrow_down:

[lengrongfu]

OK, the current documentation looks pretty good, I'll close this PR.