To install, point your browser at the installation url:
  /admin/install
To upgrade baikal, do the same but note that starting from version 0.7.0
baikal now uses a yaml file instead of php config.  The installer will
try to convert your configuration, but fail to retain your MySQL
database config (if you use that).
  https://github.com/sabre-io/Baikal/issues/943
Simply edit the /etc/baikal/baikal.yaml file and add the missing values
under the database section.