Docs/GitHub app instructions

[baristaGeek]

I was having some trouble with the GitHub application setup step for developing locally.

I added the steps that I used to get this working as instructions. Hope it makes it more friendly for more contributors.

[vercel[bot]]

@baristaGeek is attempting to deploy a commit to the Elegance Team on Vercel.

A member of the Team first needs to authorize it.

[CLAassistant]

All committers have signed the CLA.

[steven-tey]

Thank you for this! We moved our docs repo to https://github.com/dubinc/docs – do you mind making the same PR there instead?