Better document OEM supported Heads forks vs Heads rolling releases community support

[tlaurion]

Question asked today, base for documentation writing on matrix Heads channel

Threads:

• Heads' Matrix community channel thread
• Dasharo Premier Support's Matrix channel - accessible only through subscription

Notes:

• nv41 bought from clevo directly is said to most probably be Bootguarded, and hence might not be flashable with coreboot+heads.