extra-apps.md: Document limitations of raspberrypi3-64

Signed-off-by: Khem Raj <raj.khem@gmail.com>

docs/extra-apps.md

@@ -7,3 +7,9 @@ able to compile omxplayer you will need to whiteflag the commercial
 license in your local.conf:
 
     LICENSE_FLAGS_WHITELIST = "commercial"
+## raspberrypi3-64
+
+Currently, raspberrypi3-64 does not boot into graphics, this needs more investigation
+and fixes, until then none of images using graphics stack would boot into UI, although
+the system would be up and ready, graphics wont come up. One can use serial console or
+remote login to get into system