Improve CONTRIBUTING.md

[cspotcode]

#1664 (comment)

[codecov]

Codecov Report

Merging #1678 (c1dd857) into main (20cbbf5) will increase coverage by 0.59%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
src/configuration.ts	91.07% <0.00%> (-0.60%)	⬇️
src/transpilers/swc.ts	75.47% <0.00%> (ø)
src/bin-esm.ts	100.00% <0.00%> (ø)
src/child/spawn-child.ts	75.00% <0.00%> (ø)
src/child/child-require.ts	41.66% <0.00%> (ø)
src/child/child-loader.ts	88.88% <0.00%> (ø)
src/child/child-entrypoint.ts	91.66% <0.00%> (ø)
src/repl.ts	82.29% <0.00%> (+0.17%)	⬆️
src/index.ts	78.52% <0.00%> (+0.55%)	⬆️
src/esm.ts	83.33% <0.00%> (+0.64%)	⬆️
... and 2 more