Minor corrections to the contrib-guide

[Till Rettig]

Hi John,
first time I consulted the contributor's guide. It's now much easier to 
read than the old text file. Some things made me stumbel upon, though:

in 3.7.2 Documentation translation details you have different starting 
points for the individual files: mostly you start from LL-directory, but 
then it should be also ../po/lilypond-doc.pot and 
../../lilypond-texi2html.init

The last was what made me stumble -- I never remember that I have 
translated it -- isn't this done from the .po-file? At least that is 
what I thought.

After the lilypond-texi2html.init file you write (see TRANSLATION), do 
you refer to the old text file that got deleted?

A bit later there is mentioned the install.itely -- didn't it get parted 
into install and compile?

In the section Maintaining without updating translations there are some 
orthography mistakes -- you will spot them more quickly yourself. (The 
last sentence in the third paragraph is double.)

Didn't find anymore mistakes :-)

Greetings
Till