Fix link to Auth Guide in readme

[asherf]

Summary

Fix link to Auth Guide in readme
Before:

After:

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #498 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #498   +/-   ##
=======================================
  Coverage   69.58%   69.58%           
=======================================
  Files          15       15           
  Lines        1654     1654           
  Branches       91       91           
=======================================
  Hits         1151     1151           
  Misses        481      481           
  Partials       22       22

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[RodneyU215]

Thank you @asherf!