Proposal: Slack channel for manim

Since manim is getting overwhelming popularity (13k+ stars on GitHub :hushed: ) I think it would be a good idea to have a `Slack/Gitter/IRC/**` channel for manim for quick resolution of number of problems that are faced by the users everyday. (Since there's no particular fourm per se, some of the issues are users trying to ask if can be done with manim).


Also, it would be really helpful for people who are starting out with manim (or facing common installation errors in manim)