Document that euler angles should be in radians for quaternion constructor

[adlarkin]

Signed-off-by: Ashton Larkin 42042756+adlarkin@users.noreply.github.com

Summary

To help remove confusion for users, I added a note that the quaternion constructor that takes a euler angle vector expects the angles to be in radians.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

Merging #298 (4269706) into ign-math6 (afd0b22) will not change coverage.
The diff coverage is n/a.

❗ Current head 4269706 differs from pull request most recent head a1aeb21. Consider uploading reports for the commit a1aeb21 to get more accurate results

@@            Coverage Diff             @@
##           ign-math6     #298   +/-   ##
==========================================
  Coverage      99.65%   99.65%           
==========================================
  Files             67       67           
  Lines           6359     6359           
==========================================
  Hits            6337     6337           
  Misses            22       22           

Impacted Files	Coverage Δ
include/ignition/math/Quaternion.hh	100.00% <ø> (ø)

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[osrf-triage]

This pull request has been mentioned on Gazebo Community. There might be relevant details there:

https://community.gazebosim.org/t/new-ignition-releases-2022-03-01-citadel-edifice-fortress/1313/1