docs: setup documentation with mkdocs

[tlambert03]

This adds documentation that we can build on. I don't want to spend too much time evaluating this specific PR. So will likely merge soon. but every part of this is open for subsequent refactoring. It includes a nice install table:

and complete API documentation:

[codecov]

Codecov Report

Attention: Patch coverage is 88.46154% with 3 lines in your changes missing coverage. Please review.

Project coverage is 70.19%. Comparing base (48d06d4) to head (e5874ab).
Report is 23 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ndv/views/_vispy/_histogram.py	0.00%	2 Missing ⚠️
src/ndv/views/_app.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
- Coverage   70.53%   70.19%   -0.34%     
==========================================
  Files          43       44       +1     
  Lines        4253     4255       +2     
==========================================
- Hits         3000     2987      -13     
- Misses       1253     1268      +15     

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