added CONTRIBUTING section to HACKING.txt (atm only: how to run tests)
added CONTRIBUTING section to HACKING.txt (atm only: how to run tests)

oneclickorgs/one-click-orgs-deployment,oneclickorgs/one-click-orgs,oneclickorgs/one-click-orgs-deployment,oneclickorgs/one-click-orgs,emmapersky/one-click-orgs,oneclickorgs/one-click-orgs-deployment,oneclickorgs/one-click-orgs,emmapersky/one-click-orgs,oneclickorgs/one-click-orgs