docs: add readme

Author: pipech

raven/omni_channel_chat/README.md

@@ -0,0 +1,36 @@
+## Feature
+
+### Messaging
+
+|             | Line | Facebook |
+|-------------|------|----------|
+| Incoming    |      |          |
+|   Message   |      |          |
+|     Text    | Y    | Y        |
+|     Image   | Y    | Y        |
+|     File    | Y    | Y        |
+|     Sticker | TODO | Y        |
+|   Feature   |      |          |
+|     Reply   | TODO | TODO     |
+| Outgoing    |      |          |
+|   Message   |      |          |
+|     Text    | Y    | Y        |
+|     Image   | *1   | *1       |
+|     File    | *1   | *1       |
+|   Feature   |      |          |
+|     Reply   | TODO | TODO     |
+
+**Remark**
+
+1. Public / Private file has to be handle properly, currently files upload to raven will be private file but chat required it to be private.
+
+## TODO
+
+### UX/UI
+
+- [ ] Create Omni-Channel Chat interface for mobile
+
+### Provider
+
+- [ ] Instagram
+- [ ] WhatsApp