[doc] Show how to bootstrap an isolated buildout

doc/getting-started.rst

@@ -102,6 +102,33 @@ specified using *parts*.  The parts to be built are listed in the
 name that specifies the software to build the part and provides
 parameters to control how the part is built.
 
+
+Bootstrapping an isolated environment
+=====================================
+
+Sometimes it is useful to install ``zc.buildout`` and its dependencies
+directly in ``eggs`` directory and to generate a ``buildout`` script in
+the ``bin`` directory that uses the version in ``eggs`` directory,
+instead of relying on the package available in the environment.
+
+One way to achieve this uses the ``extra-paths`` option of ``buildout``
+section: by setting it to empty value, packages outside of ``eggs``
+or ``develop-eggs`` directories will not be considered when looking
+for already installed eggs. Then the ``bootstrap`` command will
+install ``zc.buildout`` and its dependencies from scratch in ``eggs``.
+
+.. code-block:: console
+
+  buildout buildout:extra-paths= bootstrap
+
+After this, the generated ``bin/buildout`` script will use the packages
+installed in ``eggs`` directory instead of those in the environment and
+preserve the isolation from the environment, even without setting
+``extra-paths``. That is because the default value for ``extra-paths``
+only considers the paths where ``zc.buildout`` and its dependencies are
+found, and in this case that is only the ``eggs`` directory.
+
+
 Installing software
 ===================