Add conda-forge to README and change wording in docs.

[tobiasraabe]

• Add conda-forge to README
• Highlight importance of correctly specifying dependencies.

[codecov]

Codecov Report

Merging #72 (d4a6e0b) into main (b80437e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #72   +/-   ##
=======================================
  Coverage   90.05%   90.05%           
=======================================
  Files          55       55           
  Lines        4596     4596           
=======================================
  Hits         4139     4139           
  Misses        457      457           

Flag	Coverage Δ
end_to_end	75.84% <ø> (ø)
integration	41.94% <ø> (ø)
unit	68.77% <ø> (ø)

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