README contains stale base-org references that should point to base org

[Sertug17]

Noticed the README still references the old base-org GitHub org in several places. The org moved to base a while ago.

Affected lines:

• Line 7: base-org/contract-deployments link
• Lines 11-15, 27-28: Shield badge URLs using base-org/contracts

Happy to send a PR with the fixes!

[schoolkamsergj]

I'd like to work on this. I'll fix all the stale base-org references
in the README to point to the correct base org. Will open a PR shortly.