Short PR to address 2 minor documentation issues

[desilinguist]

This PR closes #512 and closes #680.

• Update CONTRIBUTING.md file to fix the git push instructions (Issue: #512)
• Add a link to RSMTool’s QWK implementation from the SKLL documentation. We do this instead of moving RSMTool’s QWK implementation to SKLL because that is no longer necessary now that SKLL supports custom metrics. (Issue: #680)

[codecov[bot]]

Codecov Report

Merging #704 (700644f) into main (1d01a43) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #704   +/-   ##
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  Coverage   96.89%   96.89%           
=======================================
  Files          63       63           
  Lines        9213     9213           
=======================================
  Hits         8927     8927           
  Misses        286      286           

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