[Feature Request] Add Info Page for installer dialog

[SamPurple22]

Hi Bottles developers,

As discussed in #211, please add an Info page for Installers, where the user can easily see what the installer should do and especially if they need to perform any additional steps after running the installer or any other relevant information the installer maintainer might include.

I am thinking it could even maybe be a separate action for installer so as to no disrupt the current flow. Something like:

Steps:

• action: info_page title: "Installer X" text: | This will install X game/software. The installer requires y b x. After the installer is finished, please run the following script manually: !bottle_drive/script1.sh