Improve Documentation

[crisgarner]

• [x] Make sure to let coordinators know that the example files are for Sepolia.
• [x] Improve network documentation on MACI (users assume is optimism-sepolia instead of optimism_sepolia)
• [x] Fix broken links with new docs page

[crisgarner]

Fixes by https://github.com/privacy-scaling-explorations/maci-rpgf/pull/142