Adds clarification & examples to demystify Transforms. (#4653)

* Adds clarification & examples to demystify Transforms.

* Fleshes out documentation of NodeOptions for Transforms

* Update docs/concepts/04-transforms.md

Co-authored-by: Dylan Schiemann <dylan@dojotoolkit.org>

* Uses 'API' in the title of all API documents

Co-authored-by: Dylan Schiemann <dylan@dojotoolkit.org>

docs/api/nodes/README.md

@@ -1,4 +1,4 @@
-# Node Types
+# Node Types APIs
 
 The `Node` union type represents all of the different types of nodes that occur in a Slate document tree.
 

docs/api/nodes/editor.md

@@ -1,6 +1,6 @@
-# Editor
+# Editor API
 
-The `Editor` object stores all the state of a slate editor. It can be extended by plugins to add helpers and implement new behaviors.
+The `Editor` object stores all the state of a Slate editor. It can be extended by [plugins](../../concepts/08-plugins.md) to add helpers and implement new behaviors. It's a type of `Node` and its path is `[]`.
 
 ```typescript
 interface Editor {

docs/api/nodes/element.md

@@ -1,6 +1,6 @@
-# Element
+# Element API
 
-`Element` objects are a type of node in a Slate document that contain other `Element` nodes or `Text` nodes.
+`Element` objects are a type of `Node` in a Slate document that contain other `Element` nodes or `Text` nodes.
 
 ```typescript
 interface Element {

docs/api/nodes/node-entry.md

@@ -1,6 +1,6 @@
-# NodeEntry
+# NodeEntry API
 
-`NodeEntry` objects are returned when iterating over the nodes in a Slate document tree. They consist of the node and its `Path` relative to the root node in the document.
+`NodeEntry` objects are returned when iterating over the nodes in a Slate document tree. They consist of an array with two elements: the `Node` and its `Path` relative to the root node in the document.
 
 They are generics meaning that sometimes they will return a subset of `Node` types like an `Element` or `Text`.
 

docs/api/nodes/node.md

@@ -1,4 +1,4 @@
-# Node
+# Node API
 
 - [Static methods](node.md#static-methods)
   - [Retrieval methods](node.md#retrieval-methods)

docs/api/nodes/text.md

@@ -1,4 +1,4 @@
-# Text
+# Text API
 
 `Text` objects represent the nodes that contain the actual text content of a Slate document along with any formatting properties. They are always leaf nodes in the document tree as they cannot contain any children.