Update docs for plugin devel (#268)

docs/architecture/index.md

@@ -45,8 +45,6 @@ Plugin source bridge is dispatching received source events to all configured com
 
 Source is a binary that implements the [source](https://github.com/kubeshop/botkube/blob/main/proto/source.proto) Protocol Buffers contract. Source starts asynchronous streaming of domain-specific events. For example, streaming Kubernetes events.
 
-The `kubernetes` is a built-in Botkube source. It will be extracted in the future Botkube releases.
-
 ### Bot
 
 Bot represents a bidirectional communication platform. Each bot is responsible for authenticating, managing connections, and providing an interface for receiving and sending messages for a given platform like Slack, Discord, etc. Connection is mostly done via WebSocket.

docs/plugin/custom-source.md

@@ -232,4 +232,4 @@ sources:
         interval: 2m
 ```
 
-This means that two different `botkube/ticker` plugin configurations were bound to the `all-teams` Slack channel. Under `source.StreamInput{}.Configs`, you will find the list of configurations in the YAML format as specified under the `config` property for each bound and enabled sources. The order of the configuration is the same as specified under the `bindings.sources` property. It's up to the plugin author to merge the passed configurations. In this case, the plugin author can override the `interval` property based on the config order, so `ticker-team-b` will take precedence as the last item on the list.
+This means that two different `botkube/ticker` plugin configurations were bound to the `all-teams` Slack channel. For each bound configuration [Botkube source dispatcher](../architecture/index.md#plugin-source-bridge) calls `Stream` method with the configuration specified under the `bindings.sources` property.