Add the following to ./git/hooks/post-commit and change your UID and TOKEN (obtained from the user -> settings dialog). More information here https://github.com/lefnire/habitrpg/wiki/API

post-commit

# Gain XP on HabitRPG
HABITRPG_UID="xxxxx"
HABITRPG_TOKEN="yyyyyy"
curl -X POST -H 'Content-Type:application/json' \
"https://habitrpg.com/v1/users/${HABITRPG_UID}/tasks/git/up" \
-d "{\"apiToken\":\"${HABITRPG_TOKEN}\", \"title\":\"Git commit\", \"service\":\"git\", \"icon\":\"https://github.com/favicon.ico\"}" 1>/dev/null 2
>&1

I'm so adding this to my hook template.