Update ReadMe.md

[segun-codes]

Recommendation on command to run if step #10 (here: https://github.com/publiclab/plots2/blob/master/README.md) in the "Standard Installation" section of the ReadMe.md file returns an error (shown in the attached snapshot below), added to the existing step #10 and not as a standalone installation step. This resolution approach is based on the advice I received from @TildaUdufo.

Fixes #11466

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[Dhei-vid]

@segun-codes Please how can i contribute to this