When there are applied changes to difficulty calculation, notify users of such changes on the rank graphs

[Tenexxt]

The title is a bit convoluted so I will show a example of what I mean:

Using google trends as a example, when there were changes made to their data collection algorythms, there is a light gray "Warning" line shown on the graph, and when hovering over it, it describes what happened at that time that might alter the results going forward.

Basically, I'm suggesting something like this but for ranking graphs, since new users (or just clueless people) going into the game will be able to imiedetaly see why everyone has some "weird shuffle" on their rank on a certain period. Would also make it look more "intended", as currently all you have is the spikes, which looks kinda bugged without a direct link. (atleast i think it looks kinda bugged and think it would make it make more sense)

[peppy]

We already have a system for this, surprisingly. I don't think osu-web supports it, but old web did.