Documentation: Add guidelines on how members should show their association to coala on online platforms

Recently I came across a GitHub profile of a guy who mentioned himself as a "Maintainer @coala"
On further investigation, I found out that he was just a member of the newcomer team and wasn't even a part of the developers team. (This has already been reported to John)
We need to lay down some ground rules for our members on how they should show their association to coala on different websites. For example:
- Members of the newcomers team -> Member @coala
- Members of the developers team -> Developer @coala
- Members of the research team -> Research @coala

We need something along these lines so that we don't have members putting forth misleading/false information on their profiles.