feat(docs): migrate bs docs

blocksuite/docs-site/components/blocks/surface-block.md

@@ -0,0 +1,13 @@
+# Surface Block
+
+This is a container used to render graphical content.
+
+- In documents opened with the [edgeless editor](../editors/edgeless-editor), this block is required.
+- Its `elements` field can contain a large number of `CanvasElement`s. These elements use HTML5 canvas for rendering and can be interleaved with note blocks, with automatically flattening to use the fewest canvas contexts.
+
+![context-interleaving](../../images/context-interleaving.png)
+
+## Reference
+
+- [`SurfaceBlockSchema`](/api/@blocksuite/blocks/variables/SurfaceBlockSchema.html)
+- [`SurfaceBlockService`](/api/@blocksuite/blocks/classes/SurfaceBlockService.html)