Updates to 2012/deckmyn

Format fixes in README.md. It should be noted that in at least
deckmyn.md I was unclear about some things. It appeared the author was
using regexps but some of it looked off so I might have improperly
placed '`'s. I also am not remotely familiar with music theory or even
the terms so I could have easily missed something. I'd certainly welcome
a musician looking at and if necessary fixing it!

Renamed MANUAL to deckmyn.md.

Updated .gitignore.

Typo fixes.

2012/deckmyn/.gitignore

@@ -4,3 +4,4 @@ greensleeves.pbm
 sheetmusic.pbm
 sheetmusic.pbm
 sheetmusic.pbm
+output.pbm