Add helpful links to readme

README.md

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-# crunchtime
-Crunchtime is an open source application for planning college courses and curriculums. 
+# CrunchTime
+
+Crunchtime is a white-label application to help college students plan their class schedules each semester.
+
+See [the Wiki](https://github.com/crunch-time/crunchtime/wiki) for contribution instructions and reference information. The [backend](backend/) and [frontend](frontend/) directories have their own respective README's with more information.
+
+[Join the Slack group](https://join.slack.com/t/crunch-time-oss/shared_invite/zt-kpc8eewg-Q3VtKzuMWHTBu5xBDo51Ug) to get involved!