Clarify procedure in CONTRIBUTE.md

[E3V3A]

Please clarify the following:

1. In Step-1: What is spenrod/new-icon? (i.e. that it can be replaced by your own descriptive)
2. In Step-6: (a) Click on what? (Something missing), (b) Something funny about that whole sequence, it start with using the Github UI, then starts talking about git commands. Please specify what's to be done in GH UI vs on command line.
3. In Step-7: Please expand on what should be done here. To where and how?

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