bug#3801: 23.0.96; Emacs manual: add index entry for "notation, keys" or "key notation"

I tried looking for the place in the Emacs manual where the notation
for key sequences (the one used in the doc) is described. I tried
`notation' and found there was only one match:
`gdb-use-colon-colon-notation'. Users should be able to find this by
looking for terms such as `notation' and `conventions'.
 

In GNU Emacs 23.0.96.1 (i386-mingw-nt5.1.2600)
 of 2009-07-09 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'