Add erc4626 docs

[andrew-fleming]

Waiting on #1170.

• Documentation

[codecov]

Codecov Report

Attention: Patch coverage is 98.24561% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.62%. Comparing base (bf3d791) to head (199a8a8).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/token/src/erc20/extensions/erc4626/erc4626.cairo	97.89%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1244      +/-   ##
==========================================
+ Coverage   92.26%   92.62%   +0.35%     
==========================================
  Files          59       60       +1     
  Lines        1811     1925     +114     
==========================================
+ Hits         1671     1783     +112     
- Misses        140      142       +2     

Files with missing lines	Coverage Δ
packages/utils/src/math.cairo	100.00% <100.00%> (ø)
...s/token/src/erc20/extensions/erc4626/erc4626.cairo	97.89% <97.89%> (ø)

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