Strange documentation snippets update

[John Mandereau]

Hi Neil,

It looks like you haven't added some input/lsr/*.snippet-list or some
input/lsr/*.ly files to commit last time you used makelsr.py.  I fixed
it in a silly way, but you may want to update LSR again (and commit all
necessary files, i.e. input/lsr/*.ly and input/lsr/*.snippet-list) in
case you want indicating-cross-staff-chords-with-arpeggio-bracket.ly to
be included in Snippets with 'keyboards' tag.

Cheers,
John