Remove duplicated list of observation converters

[hkershaw-brown]

Description:

This pull request

• adds anchors to the observation converter readmes, uses these instead of relative paths to link.
• Removes the duplicate (but never in sync) list of available observation converters
• Adds a section for 'synthetic observations' because this is referenced a couple of times with in docs.
• Corrects a couple of spelling mistakes

Fixes issue

Fixes #998

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Please describe any tests you ran to verify your changes.

Built documentation locally, checked for broken links in the converter rsts. (Note there are a lot of broken links in dart because of the ../../../.html all over the code #849)

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

[mjs2369]

All the readmes for the obs converters are all in the observations/obs_converters/name_of_converter directory.

EX: observations/obs_converters/BATS/readme.rst

But the CHAMP obs converter readme is in the work dir: observations/obs_converters/CHAMP/work/README.rst

[mjs2369]

I think that these links to email the DART group should instead just list the dart email.

EX: "... is not in the repository, please email the DART
group at dart@ucar.edu"

These links open the mail app, which not everyone uses as many just use the browser.