Description of proposed changes

• readfile.read_isce_xml: bugfix when v_first=0, which is a valid value

• installation: add recommend to the pip install dev mode

Reminders

• Pass Codacy code review (green)
• Pass Circle CI test (green)
• Make sure that your code follows our style. Use the other functions/files as a basis.
• If modifying functionality, describe changes to function behavior and arguments in a comment below the function declaration.