Update 'README.md'

README.md

 
 ### **Resources:**
 * [String](https://zipcoder.github.io/reveal-slides/string-and-string-builder.html#/)
+* [Java String API](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html)
 
 ### Instructions
 1. Tests have been created for this lab