Switch to more verbose intro to bootstrap

The previous text wasn't completely true (although wasn't
misleading), and there are details in here (from HACKING) which
are useful for people to know, particularly about not storing
generated files in git.

getting-started/index.rst

@@ -146,10 +146,39 @@ Building Xapian
 Bootstrapping the code
 ~~~~~~~~~~~~~~~~~~~~~~
 
-Xapian needs to set up a few things with a fresh clone of the code, as
-well as downloading and building some tools for which we require very
-precise versions. You should run this command in the ``xapian``
-directory that was created earlier when you cloned the source code:
+The easiest way of building Xapian from git master is to use our bootstrap
+script. It takes care of a number of things which are otherwise fiddly to get
+right, including checking you have the right version of various tools we use,
+and setting up the build system for you.
+
+.. note::
+
+   One things that bootstrap does is to set up a top-level ``configure`` script
+   which ensures that the in-tree version of ``xapian-core`` is built first and
+   then used for building everything else. You almost certainly want to build
+   Xapian this way.
+
+   Not using this means you have to check by hand that you're building other
+   subdirectories against the in-tree core library, as by default they will pick
+   any installed copy. An installed copy of Xapian is likely to be a different
+   version to the source tree you are building. Building the git master version
+   of Xapian against an earlier released library will probably fail. If you're
+   working on Xapian then you almost certainly want to build everything against
+   the in-tree version, so you should use ``bootstrap`` and the ``configure``
+   script it creates.
+
+The repository does not contain any automatically generated files
+(such as ``configure``, ``Makefile.in``, Snowball-generated stemmers, Lemon-generated
+parsers, SWIG-generated code, and so on) because experience shows it's best to keep
+these out of version control.  To avoid requiring you to install the correct
+versions of the tools required, we either include the source to these tools in
+the repo directly (in the case of Snowball and Lemon), or the bootstrap script
+will download them as tarballs (autoconf, automake, libtool) or
+from git (SWIG), build them, and install them within the source tree.
+
+The bootstrap script doesn't care what the current directory is, but you
+can easily run it in the ``xapian`` directory that was created earlier when you
+cloned the source code:
 
 .. code-block:: bash