Doc: Usage 5.5, wrong file name in snippet

[Federico Bruni]

In the second snippet of code:

%%% top of file "symphony-cello.ly"
\include ../definitions.ily
\include ../Notes/cello.ily

../definitions.ily
should be replaced by
../symphonyDefs.ily

because definitions.ily is not in the directory tree

cheers,
Federico