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 e-mail 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 e-mail 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 e-mail address in Google Groups and choosing Copy link address.