Addition of upgrade info

[jake-skipper]

Summary

Addition of an Upgrades page detailing common pitfalls when upgrading from old versions of Runway.

Why This Is Needed

Some users are still on very old deployments of Runway and blocked from upgrading due to issues outlined in this new document.

Checklist

• Have you followed the guidelines in our Contribution Requirements?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Does your submission pass tests?
• Have you linted your code locally prior to submission?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?
• Have you updated documentation, as applicable?

[codecov]

Codecov Report

Merging #2021 (63d5cbd) into master (e2826b5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2021   +/-   ##
=======================================
  Coverage   90.18%   90.18%           
=======================================
  Files         247      247           
  Lines       15681    15681           
=======================================
  Hits        14142    14142           
  Misses       1539     1539           

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