Update docs for timezone abbreviations (PDT, MST, CET etc)

[systemcatch]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• [ ] 🧪 Added tests for changed code.
• [ ] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [ ] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [ ] 📚 Updated documentation for changed code.
• [ ] ⏩ Code is up-to-date with the master branch.

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

closes #835

[codecov[bot]]

Codecov Report

Merging #836 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #836   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines         1776      1776           
  Branches       306       306           
=========================================
  Hits          1776      1776           

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 5e2e52a...f431a22. Read the comment docs.

[systemcatch]

Hey @jadchaar I updated the wording, let me know if you're happy with it.