update building instructions

README.rst

@@ -230,19 +230,21 @@ required:
    (normally `/usr/local`) or in the prefix specified by the `--prefix`
    argument to `configure`.
 
-Building the varnish module (vmod)
-----------------------------------
+Building the varnish module (vmod) for Varnish 4 and higher
+-----------------------------------------------------------
 
-To build the vmod, in addition to the `configure` arguments given
-above, the `VARNISHSRC` argument must be used as in
+If varnish is installed in a standard directory, generic :ref:BUILDING
+as explained above should also build the vmod.
+
+If you have installed Varnish to a non-standard directory, call
+``autogen.sh`` and ``configure`` with ``PKG_CONFIG_PATH`` pointing to
+the appropriate path. For example, when varnishd configure was called
+with ``--prefix=$PREFIX``, use
 
 ::
 
-	sh configure DCS_KEY=<key> DCS_ACCOUNT=<account-name> \
-	   VARNISHSRC=/path/to/your/varnish/source/varnish-cache
-
-Optionally, a custom vmod installation directory can be specified
-using `VMOD_DIR=<dir>`
+   PKG_CONFIG_PATH=${PREFIX}/lib/pkgconfig
+   export PKG_CONFIG_PATH
 
 When building the vmod, an additional
 
@@ -252,6 +254,21 @@ When building the vmod, an additional
 
 step is recommended to run the bundled `varnishtest` tests.
 
+Building the varnish module (vmod) for Varnish 3
+------------------------------------------------
+
+To build the vmod for varnish 3, in addition to the `configure`
+arguments given above, the `VARNISHSRC` argument must be used as in
+
+::
+
+	sh configure DCS_KEY=<key> DCS_ACCOUNT=<account-name> \
+	   VARNISHSRC=/path/to/your/varnish/source/varnish-cache
+
+Optionally, a custom vmod installation directory can be specified
+using `VMOD_DIR=<dir>`
+
+
 Building for use with Varnish 2
 -------------------------------