[PATCH] dev-manual: Emphasize that use of Subversion is uncommon

At the moment, there does not appear to be a single use of Subversion
in numerous OE layers, so mention that it is effectively deprecated as
an SCM even though it is still supported.

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

---

diff --git a/documentation/dev-manual/external-scm.rst b/documentation/dev-manual/external-scm.rst
index 3ca9079b3..c22456aef 100644
--- a/documentation/dev-manual/external-scm.rst
+++ b/documentation/dev-manual/external-scm.rst
@@ -11,6 +11,13 @@ This only works for SCMs from which it is possible to get a sensible
 revision number for changes. Currently, you can do this with Apache
 Subversion (SVN) and Git.

+.. note::
+
+   While OpenEmbedded still actively maintains a Subversion package and
+   its underlying ``svn`` fetcher in Bitbake and you can still use
+   Subversion for custom recipes, its use is no longer common in
+   standard layers.
+
 To enable this behavior, the :term:`PV` of
 the recipe needs to include a ``+`` sign in its assignment.
 Here is an example::