update CONTRIBUTING.md

[jhuleatt]

Add instructions to run:

yarn build
yarn test
yarn lint
yarn docs

before committing

[justjish]

Might want to clarify that forked repos typically require the following to be added to the typedoc args --gitRemote upstream

so in full it would be
typedoc --options typedoc.json --gitRemote upstream && markdown-toc -i docs/use.md

[jhuleatt]

Might want to clarify that forked repos typically require the following to be added to the typedoc args --gitRemote upstream

so in full it would be
typedoc --options typedoc.json --gitRemote upstream && markdown-toc -i docs/use.md

Great point, I've added a new yarn docs:fork command and added it to the Before submitting a PR instructions.