Update documentation: CRF works with AOM_Q mode

Tested that if AOM_Q is set, this variable will still be used
to pull the CRF value.

Change-Id: Ie99f56bcafef021ad452acdacd69586b4ec2e260

aom/aomcx.h

diff --git a/aom/aomcx.h b/aom/aomcx.h
index 8e42bd6..e88607f 100644
--- a/aom/aomcx.h
+++ b/aom/aomcx.h
@@ -218,10 +218,10 @@
    */
   AOME_SET_TUNING = AOME_SET_ARNR_STRENGTH + 2,
 
-  /*!\brief Codec control function to set constrained quality level.
+  /*!\brief Codec control function to set constrained / constant quality level.
    *
    * \attention For this value to be used aom_codec_enc_cfg_t::rc_end_usage
-   *            must be set to #AOM_CQ.
+   *            must be set to #AOM_CQ or #AOM_Q.
    * \note Valid range: 0..63
    */
   AOME_SET_CQ_LEVEL,