Document LFX Mentees shouldn't contact the projects directly

[xmulligan]

When the LFX program is open and the projects are up, a lot of the potential mentees contact the mentors directly trying to get their applications ahead of the others. This puts a lot of load on the mentors before the project is even started and discourages projects to apply again in the futre. It can also be disruptive to the work the project is doing. I've had probably 30 people contact me directly about the Cilium mentorship. It would be great to document that potential mentees should just apply through the platform rather than trying to get their application ahead.