Point README COPYING link to main; not master

[xlxs4]

As per #1119.

[codecov]

Codecov Report

Merging #1121 (3570d5f) into main (c5106d6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1121   +/-   ##
=======================================
  Coverage   90.02%   90.02%           
=======================================
  Files          73       73           
  Lines        3861     3861           
  Branches      330      330           
=======================================
  Hits         3476     3476           
  Misses        297      297           
  Partials       88       88           

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[xlxs4]

Couldn't understand exactly why requests failed, shouldn't have to do with the PR

[jorgepiloto]

Hi @xlxs4,

thanks for addressing this. You are right, the error is not related to the actual changes but to some "timeout" exception when requesting data from NASA server. Thus, let us merge this 🚀