updated CHANGELOG with sync/async frame processors

CHANGELOG.md

@@ -9,20 +9,39 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
-- Added `CartesiaHttpTTSService`. This is a synchronous frame processor
-  (i.e. given an input text frame it will wait for the whole output before
-  returning).
+- Pipecat has a pipeline-based architecture. The pipeline consists of frame
+  processors linked to each other. The elements traveling across the pipeline
+  are called frames.
 
-- A clock can now be specified to `PipelineTask` (defaults to
-  `SystemClock`). This clock will be passed to each frame processor via the
-  `StartFrame`.
+  To have a deterministic behavior the frames traveling through the pipeline
+  should always be ordered, except system frames which are out-of-band
+  frames. To achieve that, each frame processor should only output frames from a
+  single task.
+
+  In this version we introduce synchronous and asynchronous frame
+  processors. The synchronous processors push output frames from the same task
+  that they receive input frames, and therefore only pushing frames from one
+  task. Asynchronous frame processors can have internal tasks to perform things
+  asynchronously (e.g. receiving data from a websocket) but they also have a
+  single task where they push frames from.
+
+  By default, frame processors are synchronous. To change a frame processor to
+  asynchronous you only need to pass `sync=False` to the base class constructor.
 
 - Added pipeline clocks. A pipeline clock is used by the output transport to
   know when a frame needs to be presented. For that, all frames now have an
   optional `pts` field (prensentation timestamp). There's currently just one
   clock implementation `SystemClock` and the `pts` field is currently only used
   for `TextFrame`s (audio and image frames will be next).
 
+- A clock can now be specified to `PipelineTask` (defaults to
+  `SystemClock`). This clock will be passed to each frame processor via the
+  `StartFrame`.
+
+- Added `CartesiaHttpTTSService`. This is a synchronous frame processor
+  (i.e. given an input text frame it will wait for the whole output before
+  returning).
+
 - `DailyTransport` now supports setting the audio bitrate to improve audio
   quality through the `DailyParams.audio_out_bitrate` parameter. The new
   default is 96kbps.