add guild-cache tag

[Wolvinny]

There's often a lot of confusion on what is cached (by the Guilds intent) and what is not. I didnt really know how to word the 'remove the possible null', so feel free to suggest any changes

[almostSouji]

I understand the idea of the tag, but in Discord, this is just a weirdly formatted wall of words in chunks that don't necessarily relate to each other. Stuffing this all together in one place like this seems like the wrong approach to me.