Updated BUILD.md

Added a note that running `buildroot.md` may be skipped.
Updated CONTRIBUTING.md

Corrected typos.
Created ELECTRON.md

Created a separate project-related document
Revert "Updated BUILD.md"

This reverts commit 0a5ab8aa1fe5e3f371ed7123e6741ba8a53a2976.
Merge pull request #5 from Mausy5043/review-md-files

Updated md files