Add link to Java regex Pattern documentation to language.rst

Co-authored-by: Shati Patel <42641846+shati-patel@users.noreply.github.com>

Author: Marcono1234

docs/language/ql-handbook/language.rst

@@ -1761,6 +1761,7 @@ The following built-in predicates are members of type ``string``:
 +----------------------+-------------+------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 
 Regular expressions are as defined by ``java.util.regex.Pattern`` in Java.
+For more information, see the `Java API Documentation <https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/regex/Pattern.html>`__.
 
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