add scalability experiment

cmake: -DCONFIG_SCALABILITY=1

Change-Id: Ifa908f809bcf904bdf0ed87b351e1ef3accc2b3f
diff --git a/docs.cmake b/docs.cmake
index 7fc7563..aa4cf16 100644
--- a/docs.cmake
+++ b/docs.cmake
@@ -89,6 +89,16 @@
       "Simplified encoder loop."
       "Two-pass encoder loop.")
 
+  if (CONFIG_SCALABILITY)
+    set(AOM_DOXYGEN_EXAMPLE_SOURCES
+        ${AOM_DOXYGEN_EXAMPLE_SOURCES}
+        "${AOM_ROOT}/examples/scalable_encoder.c")
+
+    set(AOM_DOXYGEN_EXAMPLE_DESCRIPTIONS
+        ${AOM_DOXYGEN_EXAMPLE_DESCRIPTIONS}
+        "Scalable encoder loop.")
+  endif ()
+
   set(AOM_DOXYGEN_SECTIONS ${AOM_DOXYGEN_SECTIONS} "av1_encoder encoder")
 
   set(AOM_DOXYGEN_SOURCES