[core] Reformat send messages documentation

docs/site/content/en/docs/how-to/send-messages/index.md

@@ -15,18 +15,30 @@ If you haven't yet - please follow the steps from [**Quick Start →**]({{< relr
 
 ## Fields
 There are common fields that you can find in almost all requests:
-- `session` - a session name from which account you're sending the message. We use `default` in the examples.
-  - Core ![](/images/versions/core.png) version supports only `default` session.
-  - Plus ![](/images/versions/plus.png) allows you to run multiple sessions inside one container to save your memory and CPU resources!
+```json
+{
+  "session": "default",
+  "chatId": "12132132130@c.us",
+  "file": "..."
+}
+```
+
+### session
+`session` - a session name from which account you're sending the message. We use `default` in the examples.
+- Core ![](/images/versions/core.png) version supports only `default` session.
+- Plus ![](/images/versions/plus.png) allows you to run multiple sessions inside one container to save your memory and CPU resources!
+
 Read more about [multiple sessions →]({{< relref "/docs/how-to/sessions" >}})
 
-- `chatId` - it's a phone number or Group identifier where you're sending the message.
-  - **Phone numbers** accounts use international phone number without + at the start and add `@c.us` at the end.
-    For phone number `12132132131` the `chatId` is  `12132132131@c.us`.
-  - **Groups** use random number with `@g.us` at the end.
+### chatId
+`chatId` - it's a phone number or Group identifier where you're sending the message.
+- **Phone numbers** accounts use international phone number without + at the start and add `@c.us` at the end.
+  For phone number `12132132131` the `chatId` is  `12132132131@c.us`.
+- **Groups** use random number with `@g.us` at the end.
 
+### file
 When sending media (images, voice, files) you can either use:
-- `file.data` field with base64 encoded file (https://base64.guru/converter/encode/file)
+- `file.data` field [with base64 encoded file](https://base64.guru/converter/encode/file)
 - `file.url` field with public available URL for that file
 
 ## Endpoints