docs: update descriptions and README

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Author: zimeg

block-kit/README.md

@@ -19,4 +19,6 @@ Read the [docs](https://docs.slack.dev/block-kit/) to learn concepts behind thes
 - **[Markdown](https://docs.slack.dev/reference/block-kit/blocks/markdown-block)**: Displays formatted markdown. [Implementation](./src/blocks/markdown.py).
 - **[Rich text](https://docs.slack.dev/reference/block-kit/blocks/rich-text-block)**: Displays formatted, structured representation of text. [Implementation](./src/blocks/rich_text.py).
 - **[Section](https://docs.slack.dev/reference/block-kit/blocks/section-block)**: Displays text, possibly alongside elements. [Implementation](./src/blocks/section.py).
+- **[Plan](https://docs.slack.dev/reference/block-kit/blocks/plan-block)**: Displays a collection of related tasks. [Implementation](./src/blocks/plan.py).
+- **[Task card](https://docs.slack.dev/reference/block-kit/blocks/task-card-block)**: Displays a single task, representing a single action. [Implementation](./src/blocks/task_card.py).
 - **[Video](https://docs.slack.dev/reference/block-kit/blocks/video-block)**: Displays an embedded video player. [Implementation](./src/blocks/video.py).

block-kit/src/blocks/plan.py

@@ -7,8 +7,7 @@
 
 def example01() -> PlanBlock:
     """
-    Displays a plan with multiple task cards representing a sequence of actions.
-    This is an experimental block type that requires a toggle to preview.
+    Displays a collection of related tasks.
     https://docs.slack.dev/reference/block-kit/blocks/plan-block/
 
     A plan block with multiple task cards in various states.

block-kit/src/blocks/task_card.py

@@ -8,8 +8,7 @@
 
 def example01() -> TaskCardBlock:
     """
-    Displays a single task which represents a single action.
-    This is an experimental block type that requires a toggle to preview.
+    Displays a single task, representing a single action.
     https://docs.slack.dev/reference/block-kit/blocks/task-card-block/
 
     A task card with output and sources.