Document mentors for new contributors

We’ve created a list of possible mentors to help new contributors gain independence while having a person to talk to. This needs to be documented somewhere.

At first sight we could add this to the" talk to us" section on https://tails.boum.org/contribute/how/code/#index6h1

Feature Branch: doc/10179-mentors

Related issues

Related to #7047 (closed)
Related to #10708 (closed)
Has duplicate #11772 (closed)

Original created by @u on 10179 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information