Depend on numpy>=1.21 to fix installation issue

[itcarroll]

• Closes import error caused by old numpy version #587
• Tests added Not sure how to write a test for an installation. Checks out locally with poetry though.
• Fully documented, including docs/history.rst for all changes and docs/rioxarray.rst for new API

[codecov]

Codecov Report

Base: 95.90% // Head: 95.90% // No change to project coverage 👍

Coverage data is based on head (afcf16f) compared to base (9d59756).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #636   +/-   ##
=======================================
  Coverage   95.90%   95.90%           
=======================================
  Files          12       12           
  Lines        1735     1735           
=======================================
  Hits         1664     1664           
  Misses         71       71           

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[itcarroll]

Check failure appears unrelated to me. Anaconda's nightly scipy looks pinned to an old version of setuptools ... maybe?

[snowman2]

Thanks @itcarroll 👍