Docs: add installation guide for openSUSE

[jenting]

What is the purpose of this change? What does it change?

Add installation guide on openSUSE.

Fix #2115

Checklist

• I have read the Contribution Guidelines
• I have added tests for all changes in this PR
• I have added documentation for the changes (in the manual)
• There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• I have run gofmt on the code in all commits
• All commit messages are formatted in the same style as the other commits in the repo
• I'm done, this Pull Request is ready for review

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@604b18a). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2456   +/-   ##
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  Coverage          ?   47.06%           
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  Files             ?      178           
  Lines             ?    14516           
  Branches          ?        0           
=========================================
  Hits              ?     6832           
  Misses            ?     6665           
  Partials          ?     1019

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[rawtaz]

Thanks!