Update the description for AV1E_GET_SEQ_LEVEL_IDX

Change-Id: Ie41b51c6326104e94c1d8bbec6cd3f44d3e0f21d
diff --git a/aom/aomcx.h b/aom/aomcx.h
index bf21285..b424c3c 100644
--- a/aom/aomcx.h
+++ b/aom/aomcx.h
@@ -528,7 +528,9 @@
    */
   AV1E_SET_TARGET_SEQ_LEVEL_IDX,
 
-  /*!\brief Codec control function to get sequence level index.
+  /*!\brief Codec control function to get sequence level index for each
+   * operating point. There can be at most 32 operating points. The results will
+   * be written into a provided integer array of sufficient size.
    */
   AV1E_GET_SEQ_LEVEL_IDX,