bitbake: bitbake-user-manual-metadata: include a space on a append example

By definition, the override operator "_append" does not include a space,
so include it.

(Bitbake rev: 6775e2de9067d8f472d7bfb5b78ec835a5688755)

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/doc/bitbake-user-manual/bitbake-user-manual-metadata.xml

@@ -669,7 +669,7 @@
                         <literallayout class='monospaced'>
      DEPENDS = "glibc ncurses"
      OVERRIDES = "machine:local"
-     DEPENDS_append_machine = "libmad"
+     DEPENDS_append_machine = " libmad"
                         </literallayout>
                         In this example, <filename>DEPENDS</filename> becomes
                         "glibc ncurses libmad".