[doc] Improve contributing documents and add a script for check commit.

[jolestar]

1. Add a script for fast check the commit.
2. Add Contribution Guide and Code of Conduct.
3. Add Issue and Pull request template.

[codecov]

Codecov Report

Merging #3213 (3c51544) into master (274f8dd) will increase coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3213      +/-   ##
==========================================
+ Coverage   32.07%   32.15%   +0.08%     
==========================================
  Files         503      503              
  Lines       46326    46326              
  Branches    21247    21247              
==========================================
+ Hits        14855    14892      +37     
+ Misses      17457    17414      -43     
- Partials    14014    14020       +6     

Flag	Coverage Δ
unittests	32.15% <ø> (+0.08%)	⬆️

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

Impacted Files	Coverage Δ
...m/types/src/account_config/events/config_change.rs	66.67% <0.00%> (-33.33%)	⬇️
network-p2p/src/transport.rs	15.10% <0.00%> (-9.43%)	⬇️
vm/natives/src/account.rs	25.00% <0.00%> (-6.25%)	⬇️
vm/types/src/transaction_metadata.rs	56.72% <0.00%> (-5.97%)	⬇️
storage/src/db_storage/mod.rs	44.50% <0.00%> (-4.78%)	⬇️
vm/types/src/token/token_code.rs	36.48% <0.00%> (-3.52%)	⬇️
network/src/worker.rs	30.65% <0.00%> (-3.22%)	⬇️
vm/types/src/token/stc.rs	62.86% <0.00%> (-2.85%)	⬇️
rpc/server/src/rate_limit_middleware.rs	19.52% <0.00%> (-2.43%)	⬇️
vm/natives/src/token.rs	28.89% <0.00%> (-2.22%)	⬇️
... and 67 more

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