[Wiki] About $dir in Pre/Post (un)install scripts

[lewis-yeung]

In Pre/Post (un)install scripts, it says that $dir will expand to the path of the app's current directory. However only in a post_install script will it actually expand to the path of current, but in the other three and the installer script, it expands to the path of the actual version directory. I think there should be detailed descriptions for this.

[rashil2000]

Updated https://github.com/ScoopInstaller/Scoop/wiki/Pre-Post-(un)install-scripts/_compare/2463bf11d7a83acaa9365b85d29a12987d79e5c4