Add compose key sequences reference

[qirlib]

Compose key is an alternative system to Windows Alt codes. On my Linux system, I use AltGr+ - - - to write em dash ­—, AltGr+ s s to write ß, AltGr + " u to write ü, AltGr+ o o to write degree sign ° and so on.

I would also appreciate if this reference was more easily accessible and not buried in the Technical Information section. Can you place it and the Windows Alt codes to the right of the title on the symbol page or under the symbol itself?