add step-by-step highlights to readme

README.md

@@ -999,6 +999,10 @@ function Example() {
 
 <img width="300" alt="line-numbers" src="https://user-images.githubusercontent.com/629429/55332077-eb3c4780-5494-11e9-8854-ba33cd0fa740.png">
 
+#### Step-by-step Highlights
+
+You can step through multiple code highlights on the same code block. Delimit each of your highlight steps with the `|` character. For example `data-line-numbers="1|2-3|4,6-10"` will produce three steps. It will start by highlighting line 1, next step is lines 2-3, and finally line 4 and 6 through 10.
+
 
 
 ### Slide number