You can install YII framework wherever you want but I recommend you to use the path
/opt/bitnami/frameworks/ since we package all the frameworks such as Symphony or Codeigniter.
Please note the frameworks mentioned are only available at LAMP Stack 5.6.X version so far. They'll be available at LAMP 7.X.X soon. See this thread for more information https://community.bitnami.com/t/how-to-use-php-frameworks-on-lamp-mamp-wamp-7-x-x/52203
Regarding where to create your YII project, you can follow the guide How To Create A Custom PHP Application?
or you can decide to replicate the structure we use for other frameworks (I would install on my laptop a LAMP 5.6.X in order to understand that structure).