It is very important to set up a method of communication for existing contributors and people who want to contribute.
Recommended would be either a Google Chat room or Google group.
Google Chat
For a Google Chat room you can pre-subscribe all the group members by inviting their group email address to the chat room. Please remember to uncheck the email notification option.
See Google Chat Help for more details.
Google Groups
To set up a Google Group, go to Google Groups and choose Create Group and follow the wizard. All Trimble groups have an associated email address which always ends in -ug@trimble.com.
See Google Chat Help for more details on using Google Groups
Remember to publish details about how to join a chat or group in the README.md for your project.
For Google Chat you can publish a link to the chat from the address bar. Assuming you have pre-subscribed as above, then anyone clicking on the link will be automatically subscribed to the chat.
For Google Groups you can publish a link by right-clicking on the group email address in Google Groups and choosing Copy link address.