[PATCH] test-manual: add more detail to the ptest section

Expand the ptest section to show how to distinguish between adding all
ptest packages to an image versus adding only a selected set of
packages to the image.

Signed-off-by: Robert P. J. Day <[email protected]>

---

  The ptest section really should be considerably longer, perhaps
using actual examples from the OE-Core code base. But I'll add just
this bit for now.

diff --git a/documentation/test-manual/ptest.rst b/documentation/test-manual/ptest.rst
index 1c946f81d..dc493b72c 100644
--- a/documentation/test-manual/ptest.rst
+++ b/documentation/test-manual/ptest.rst
@@ -31,12 +31,29 @@ see the :yocto_wiki:`Ptest </Ptest>` wiki page.
 Adding ptest to Your Build
 ==========================

-To add package testing to your build, add the :term:`DISTRO_FEATURES` and
-:term:`EXTRA_IMAGE_FEATURES` variables to your ``local.conf`` file, which
-is found in the :term:`Build Directory`::
+Adding package testing to your image is done in two steps:
+
+#. Select that all ptest packages should be built and packaged, and
+
+#. Identify which of those ptest packages to add to your image.
+
+First, in order to build all ptest packages, add the following line
+to your ``local.conf`` file::

    DISTRO_FEATURES:append = " ptest"
-   EXTRA_IMAGE_FEATURES += "ptest-pkgs"
+
+Note that this will cause all ptest packages to be built and packaged,
+but will not add any of those packages to your image; that comes in
+the next step. You can then add ptest packages to your image in one of two ways.
+
+#. If you want to add *all* of the generated ptest packages, add the line::
+
+      EXTRA_IMAGE_FEATURES += "ptest-pkgs"
+
+#. On the other hand, if you want to add only a select few of the ptest
+   packages, you can use some variation of::
+
+      IMAGE_INSTALL:append = " e2fsprogs-ptest zlib-ptest"

 Once your build is complete, the ptest files are installed into the
 ``/usr/lib/package/ptest`` directory within the image, where ``package``