Update CLA and bug bounty

[Marcono1234]

(related to #4704)

Currently CLA and bug bounty still point to Square sites:

• retrofit/website/src/content/docs/contributing.md

  Line 7 in d0b112d

  Before your code can be accepted into the project you must also sign the [Individual Contributor License Agreement (CLA)](https://squ.re/sign-the-cla).

• retrofit/.github/CONTRIBUTING.md

  Line 15 in d0b112d

  [1]: https://spreadsheets.google.com/spreadsheet/viewform?formkey=dDViT2xzUHAwRkI3X3k5Z0lQM091OGc6MQ&ndplr=1

• retrofit/BUG-BOUNTY.md

  Line 9 in d0b112d

  guidelines at https://bugcrowd.com/squareopensource

Is the CLA even still needed?
For bug bounty, respectively rather vulnerability reporting, maybe just add a SECURITY.md instead and point to GitHub's private vulnerability reporting (https://github.com/lysine-dev/<REPOSITORY>/security/advisories/new), which you have apparently already enabled.

Same applies to the other Lysine projects as well.

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Thanks for transferring these repositories to Lysine and continuing their development!

[JakeWharton]

Thanks. We're aware of this and have other changes coming along with it (like new contribution rules).