adjusted build_docs.sh for invocation from external directory

[joaquintides]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.56%. Comparing base (3fab9df) to head (9b95bef).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop      #97   +/-   ##
========================================
  Coverage    96.56%   96.56%           
========================================
  Files            5        5           
  Lines          786      786           
  Branches       233      233           
========================================
  Hits           759      759           
  Misses          27       27           

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[gennaroprota]

I guess

SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )

is a way to get the absolute path of the script. But we don't need that, so the simpler

SCRIPT_DIR=$( dirname -- "${BASH_SOURCE[0]}" )

would just be the same for us.