DOC: Contributing instructions, BytesIO, switch from rasterio, GDAL config, & external courses

[remi-braun]

• Update Contributing page with building documentation section
• Add documentation about writing into BytesIO Allow rio.to_raster with a BytesIO object #668, solves also DOC: add section on writing files in docs #584 about writing raster in the cloud
• Add a page dedicated to the switch from rasterio to rioxarray, and notably equivalences between rasterio functions and rioxarray methods
• Add a page about GDAL configuration options Does rioxarray use internal GDAL config parameters? #693
• Add and initialize external courses toctree
  • Carpentries courses DOC: link geospatial-python course in the docs #279
  • Geospatial Python courses by Earth Lab at University of Colorado, Boulder

[remi-braun]

I tried to fix some open documentation issues and propagate some user questions.
This can of course be amended by anybody, it's more of a draft right now.

Other questions :

• do you want to switch to another sphinx them?
• do you want to switch to markdown files instead of rst?

[remi-braun]

For the rasterio / rioxarray equivalences, it could be great to explain why some attributes in rasterio are becoming methods when others don't (i.e. transform). It's to preserve the lazy evaluation inherited from xarray and not recomputing on the fly these attributes when changing the raster (i.e. cropping, reprojecting...)?

[snowman2]

@remi-braun, there are some linting issues you can fix by running pre-commit run -a.

[snowman2]

Thanks @remi-braun 👍

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.55%. Comparing base (ae6635a) to head (74e1faf).
⚠️ Report is 199 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #910      +/-   ##
==========================================
- Coverage   95.90%   95.55%   -0.35%     
==========================================
  Files          12       18       +6     
  Lines        1735     2094     +359     
==========================================
+ Hits         1664     2001     +337     
- Misses         71       93      +22     

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[remi-braun]

Should I create issues relatively to the questions I had in the beginning of this PR?