Add Java 11 prerequisite
Add Java 11 prerequisite

Add sentence that Java 11 is required to run and build Closure Compiler.
google/closure-compiler,monetate/closure-compiler,monetate/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,monetate/closure-compiler,nawawi/closure-compiler,monetate/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,google/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler