Clarify documentation about source override

The current documentation about source override is ambiguous and let
users presume that you should always use "-base" after the project name
you want to override source location.

This assumption is wrong, as kolla look for a section who match exactly
the name of the image. Images who don't have a "-base", like Horizon,
are really hard to override for a user.

I propose to put an example without a "-base" and also add a disclaimer
in the documentation about that.

Change-Id: I308a352975f11c29afb3f2ea1c22212062066b4b

1 files changed, 7 insertions, 2 deletions

diff --git a/doc/source/admin/image-building.rst b/doc/source/admin/image-building.rst
index d20dff1ee..aa100f4a3 100644
--- a/doc/source/admin/image-building.rst
+++ b/doc/source/admin/image-building.rst
@@ -140,9 +140,9 @@ The ``kolla-build.conf`` file could look like this:
 .. path /etc/kolla/kolla-build.conf
 .. code-block:: ini
 
-   [glance-base]
+   [horizon]
    type = url
-   location = https://tarballs.openstack.org/glance/glance-master.tar.gz
+   location = https://tarballs.openstack.org/horizon/horizon-master.tar.gz
 
    [keystone-base]
    type = git
@@ -157,6 +157,11 @@ The ``kolla-build.conf`` file could look like this:
    type = local
    location = /tmp/ironic.tar.gz
 
+.. note::
+
+   Note that the name of the section should exactly match the image name
+   you are trying to change source location for.
+
 .. _dockerfile-customisation:
 
 Dockerfile customisation