docs(epoch-manager): add readme to epoch manager

[kerber0x]

Description and Motivation

This PR adds a readme file explaining how the epoch manager works.

Related Issues

---

Checklist:

• I have read Migaloo's contribution guidelines.
• My pull request has a sound title and description (not something vague like Update index.md)
• All existing and new tests are passing.
• I updated/added relevant documentation.
• The code is formatted properly cargo fmt --all --.
• Clippy doesn't report any issues cargo clippy -- -D warnings.
• I have regenerated the schemas if needed cargo schema.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.15%. Comparing base (0f77427) to head (1d6ffbc).
Report is 32 commits behind head on release/v2_contracts.

Additional details and impacted files

@@                   Coverage Diff                    @@
##           release/v2_contracts     #353      +/-   ##
========================================================
+ Coverage                 90.09%   91.15%   +1.06%     
========================================================
  Files                       278      279       +1     
  Lines                     29604    31119    +1515     
========================================================
+ Hits                      26673    28368    +1695     
+ Misses                     2931     2751     -180     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[0xFable]

LGTM good work, I'd love to see some more here about how we are using the epoch manager at a high level i.e the clock and how that affects other contracts

[kerber0x]

LGTM good work, I'd love to see some more here about how we are using the epoch manager at a high level i.e the clock and how that affects other contracts

Cool, will add that.