Add CLA note to top of quick-reference

[LucianaMarques]

I recently opened a PR in CPython repository. Although I did check the quick-reference steps, I did not pay attention to the fact that I had to sign a CLA before submitting my PR, even with the note there. I believe that by moving this note to the beginning of the step list would help bringing more attention to the CLA for first contributors.

Thanks!

[the-knights-who-say-ni]

Hello, and thanks for your contribution!

I'm a bot set up to make sure that the project can legally accept this contribution by verifying everyone involved has signed the PSF contributor agreement (CLA).

CLA Missing

Our records indicate the following people have not signed the CLA:

@LucianaMarques

For legal reasons we need all the people listed to sign the CLA before we can look at your contribution. Please follow the steps outlined in the CPython devguide to rectify this issue.

If you have recently signed the CLA, please wait at least one business day
before our records are updated.

You can check yourself to see if the CLA has been received.

Thanks again for the contribution, we look forward to reviewing it!