build: Add readthedocs config

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (efa7dcc) 96.71% compared to head (ee6145f) 96.71%. Report is 8 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #166 +/- ## ======================================= Coverage 96.71% 96.71% ======================================= Files 6 6 Lines 213 213 Branches 34 35 +1 ======================================= Hits 206 206 Misses 4 4 Partials 3 3 ```

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