am 698e90b1: am 27a85cca: am fb53f115: am d35c7940: am 2c31a0d7: am 9e28efe4: docs: change intro and title for contacts and sign-in lesson, and remove empty bullet

* commit '698e90b1f0fe4b105127d029c0db1aa42fd09ea9':
  docs: change intro and title for contacts and sign-in lesson, and remove empty bullet