update docs

Author: joshgoebel

src/lib/token_tree.js

@@ -70,12 +70,16 @@ class TokenTree {
   Currently this is all private API, but this is the minimal API necessary
   that an Emitter must implement to fully support the parser.
 
-  API:
+  Minimal interface:
 
   - addKeyword(text, kind)
   - addText(text)
   - addSublanguage(emitter, subLangaugeName)
   - finalize()
+  - openNode(kind)
+  - closeNode()
+  - closeAllNodes()
+  - toHTML()
 
 */
 export default class TokenTreeEmitter extends TokenTree {