Add conda-forge to README.

[tobiasraabe]

Changes

Provide a description and/or bullet points to describe the changes in this PR.

Todo

• Reference issues which can be closed due to this PR with "Closes #x".
• Review whether the documentation needs to be updated.
• Document PR in docs/changes.rst.

[codecov]

Codecov Report

Merging #11 (93495a1) into main (75e53d2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #11   +/-   ##
=======================================
  Coverage   75.30%   75.30%           
=======================================
  Files          15       15           
  Lines         409      409           
=======================================
  Hits          308      308           
  Misses        101      101           

Flag	Coverage Δ
end_to_end	59.65% <ø> (ø)
unit	69.19% <ø> (ø)

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