fix rtd build failure

[tapaswenipathak]

if triggered build from a new branch rtd build errors. could be because
it builds all files not just changed.
https://readthedocs.org/projects/openms/builds/17572157/

Closes #18.

(there were two errors in local, but the build was successful)

ReadTheDocs is not recognizing https://sphinx-inline-tabs.readthedocs.io/en/latest/usage.html#rich-tab-labels:

/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/checkouts/rtd-build-errors/docs/advanced-resources/custom-compilation.md:8: WARNING: unknown node type: <_TabInput: >

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/cmd/build.py", line 277, in build_main
    app.build(args.force_all, filenames)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/application.py", line 349, in build
    self.builder.build_update()
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/__init__.py", line 301, in build_update
    self.build(to_build,
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/__init__.py", line 367, in build
    self.write(docnames, list(updated_docnames), method)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/__init__.py", line 559, in write
    self._write_serial(sorted(docnames))
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/__init__.py", line 569, in _write_serial
    self.write_doc(docname, doctree)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/_epub_base.py", line 367, in write_doc
    super().write_doc(docname, doctree)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/builders/html/__init__.py", line 665, in write_doc
    self.docwriter.write(doctree, destination)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/writers/__init__.py", line 78, in write
    self.translate()
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/writers/html.py", line 59, in translate
    self.document.walkabout(visitor)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 227, in walkabout
    if child.walkabout(visitor):
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 240, in walkabout
    visitor.dispatch_departure(self)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/sphinx/util/docutils.py", line 583, in dispatch_departure
    super().dispatch_departure(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 2034, in dispatch_departure
    return method(node)
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 2056, in unknown_departure
    raise NotImplementedError(
NotImplementedError: <class 'sphinx.writers.html5.HTML5Translator'> departing unknown node type: _TabInput

Exception occurred:
  File "/home/docs/checkouts/readthedocs.org/user_builds/openms-staging/envs/rtd-build-errors/lib/python3.9/site-packages/docutils/nodes.py", line 2056, in unknown_departure
    raise NotImplementedError(
NotImplementedError: <class 'sphinx.writers.html5.HTML5Translator'> departing unknown node type: _TabInput
The full traceback has been saved in /tmp/sphinx-err-2btcsmzr.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

Describe the change

PR checklist

• I have added description of the change I'm proposing in the OpenMS Documentation.
• I have read and followed OpenMS Documentation Contributing guidelines.
• I have attached a screenshot of the relevant area after this change.
• CHANGELOG.md is updated.
• I have added my name in CONTRIBUTING.md.

[timosachsenberg]

wip?

[tapaswenipathak]

no, approve.

[tapaswenipathak]

(dropping any changes to {tab}, PRing separately.

diff to compare:

• success: https://readthedocs.org/projects/openms/builds/17562936/
• failure: https://readthedocs.org/projects/openms/builds/17572157/