docs: mention the gitter room in the README (#1162)
docs: mention the gitter room in the README (#1162)

Fixes #1160
alangpierce/decaffeinate,eventualbuddha/decaffeinate,decaffeinate/decaffeinate,eventualbuddha/decaffeinate,alangpierce/decaffeinate,decaffeinate/decaffeinate,alangpierce/decaffeinate