Add a note about jupyter-incubation being due a review

[krassowski]

This is a hotfix for the incubation docs being completely outdated and therefore discouraging contributions of new repositories/subprojects

• Incubator process contains archived proposal location and outdated documentation #256
• Request to move all repos from jupyter-incubator into jupyter software-steering-council-team-compass#24

Since the substantial changes will need SSC approval, I am proposing to add this note which does not modify the process itself (so does not need an SSC approval in my understanding).

[choldgraf]

LGTM - I made some minor edits and will merge! I feel comfortable "just merging" because I think this is a better reflection of current practice, and it's better to just have the docs reflect reality