Add missing c86 manual text

From http://retro.co.za/68000/CC68K/QDOSC68K/c68.txt
See ghaerr/elks#2112 (comment)

I believe this is the original c86 text manual referenced in the class,
though I don't know if there were any modifications. But the size (~146.4
KB) is close to the 147 KB expected size, so I suspect any modifications
made were small.