chore: update contributing guide

[MaikoTan]

I think there are several issues in the previous guide, so I changed the following things:

• Commonly the contributing guide is put into CONTRIBUTNIG.md not .github/contributing.md.
• Change default branch from develop to master as develop branch is no longer using.
• Use 我们 or 开发团队 to refer to our self.
• Add a code of conduct guide from Contributor Covenant.

[codecov]

Codecov Report

Merging #707 (3069b33) into master (6e3a66a) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #707      +/-   ##
==========================================
- Coverage   90.16%   90.13%   -0.04%     
==========================================
  Files          69       69              
  Lines        8146     8147       +1     
  Branches     1382     1384       +2     
==========================================
- Hits         7345     7343       -2     
- Misses        801      804       +3     

Impacted Files	Coverage Δ
plugins/frontend/console/src/http.ts	23.95% <0.00%> (-2.40%)	⬇️
plugins/mock/src/adapter.ts	100.00% <0.00%> (ø)
plugins/mock/src/webhook.ts	25.31% <0.00%> (+1.26%)	⬆️

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[shigma]

Is there anything else that prevents this PR from being ready for review?

[MaikoTan]

Is there anything else that prevents this PR from being ready for review?

Some sentences are not quite natural, but I think to give it a try is not bad.