docs: Replace docs in README with link to docs on docs.edgexfoundry.org

[lenny-goodell]

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/device-rest-go/blob/main/.github/Contributing.md

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• [x] I am not introducing a new dependency (add notes below if you are)
• [ ] I have added unit tests for the new feature or bug fix (if not, why?)
• [ ] I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• [ ] I have opened a PR for the related docs change (if not, why?)

Testing Instructions

New Dependency Instructions (If applicable)

[codecov-commenter]

Codecov Report

Merging #361 (cfd59f0) into main (47318dc) will not change coverage. The diff coverage is n/a.

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@@           Coverage Diff           @@
##             main     #361   +/-   ##
=======================================
  Coverage   32.86%   32.86%           
=======================================
  Files           2        2           
  Lines         353      353           
=======================================
  Hits          116      116           
  Misses        224      224           
  Partials       13       13