Update packages.yml (pyOpenSci#71)

Added the jointly package.

Author: arianesasso

_data/packages.yml

@@ -1,3 +1,7 @@
+- package-name: jointly
+  description: 'Jointly: A Python package for synchronizing multiple sensors with accelerometer data'
+  maintainer: ["Arne Herdick", "Felix Musmann", "Ariane Sasso", "Justin Albert", "Bert Arnrich"]
+  link: "https://github.com/hpi-dhc/jointly"
 - package-name: devicely
   description: 'Devicely: A Python package for reading, timeshifting and writing sensor data'
   maintainer: ["Ariane Sasso", "Jost Morgenstern", "Felix Musmann", "Bert Arnrich"]