Add Sphinx Docs

[jtpio]

Add skeleton for sphinx docs and RTD support

[codecov-commenter]

Codecov Report

Merging #166 (70819f5) into master (70f48ae) will increase coverage by 0.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
+ Coverage   85.27%   85.51%   +0.23%     
==========================================
  Files          17       17              
  Lines        2126     2161      +35     
  Branches      262      262              
==========================================
+ Hits         1813     1848      +35     
  Misses        220      220              
  Partials       93       93              

Impacted Files	Coverage Δ
jupyter_releaser/tests/test_cli.py	98.96% <0.00%> (+<0.01%)	⬆️
jupyter_releaser/tests/util.py	99.06% <0.00%> (+<0.01%)	⬆️
jupyter_releaser/tests/conftest.py	98.50% <0.00%> (+0.13%)	⬆️
jupyter_releaser/cli.py	90.80% <0.00%> (+0.76%)	⬆️

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[blink1073]

Thank you!