flavours: add reference to oniro-bundle-base recipe

The oniro-bundle-base recipe can be used to build a RAUC update bundle
corresponding to the oniro-image-base. By including this in the conf-notes.txt
file we surface this information where more users will see it.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>

flavours/linux/conf-notes.txt

@@ -5,6 +5,7 @@ You can now run 'bitbake <target>'
 
 Supported targets:
 - oniro-image-base
+- oniro-bundle-base
 - oniro-image-base-dev
 - oniro-image-base-tests
 - oniro-image-extra