ALSA: docs: Add toctree index entry for co-processor acceleration API

Sphinx reports missing toctree entry warning for co-processor
acceleration API docs:

Documentation/sound/designs/compress-accel.rst: WARNING: document isn't included in any toctree

Add the missing entry to fix the warning.

Fixes: 0417715 ("ALSA: compress_offload: introduce accel operation mode")
Signed-off-by: Bagas Sanjaya <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

Author: bagasme

Documentation/sound/designs/index.rst

@@ -6,6 +6,7 @@ Designs and Implementations
 
    control-names
    channel-mapping-api
+   compress-accel
    compress-offload
    timestamping
    jack-controls