Version of si which is compatible with the public preview of Textual 5

The application ID of Textual 5 is com.codeux.irc.textual5 instead of
com.codeux.irc.textual

Committing as second file because Textual 5 is not in the app store yet.
Merge pull request #3 from emsquared/master

Version of si which is compatible with the public preview of Textual 5