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 '27a85cca7c001ec47749feb60461081f14b2dfe3':
  docs: change intro and title for contacts and sign-in lesson, and remove empty bullet