Fix: Add note about backupGlobals

[localheinz]

This PR

• adds a note about @backupGlobals to README.md

[codecov]

Codecov Report

Merging #21 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #21   +/-   ##
=========================================
  Coverage     92.89%   92.89%           
  Complexity       88       88           
=========================================
  Files            11       11           
  Lines           169      169           
=========================================
  Hits            157      157           
  Misses           12       12

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