LilyPond Contributor's Guide: proposed addition
  "Introduction to LilyPond Development"

Before you start developing, it will be helpful to
understand a few basic concepts related to LilyPond
development.

The LilyPond source code is maintained as a Git repository.

A LilyPond Git repository is a directory which contains:
  1) all of the source files needed to build LilyPond, and
  2) a `.git' directory which is used by the git program to
     keep track of the data and the changes made over time.

The `official' LilyPond Git repository is hosted by the GNU
project at git.savannah.gnu.org (note that shortened form
git.sv.gnu.org resolves to the same host).  However, since
Git uses a `distributed' model, technically there is no
central repository.  Each contributor has a complete copy of
the entire repository (about 116M).  Changes made within one
contributor's copy of the repository can be shared with
other contributors using `patches'.

A `patch' is a simple text file generated by the git program
that indicates what changes have been made (using a special
format).  If a contributor's patch is approved for inclusion
(usually through the mailing list), someone on the current
development team will `apply' the patch to the official
repository.

A Git repository can be used to build (`compile') the entire
program, but it is not strictly necessary---LilyPond can be
compiled from a downloaded tarball instead.  Tarballs are
useful if you want to install the program from source files
but you don't want to do any developing.

However, a Git repository is needed to produce patches and
contribute to LilyPond development.  And even with your own
Git repository, you may choose not to compile LilyPond at
all.  In fact, compiling LilyPond is a rather involved
process, and many development tasks do not require it.
However, if you wish to see the effect of your changes on
the program itself, you will need to compile it.

To put it simply, if you only want to use the program, you
only need to *install* it.  If you want to modify source
files and create patches for development, you only need a
Git repository (technically you don't even need an installed
copy of the program, but it helps).  If you want modify
source files *and* see how your changes affect the finished
product, then you'll need a Git repository *and* you'll need
to compile the program on your own.