[RegExp] Add web demo

Author: renggli

README.md

@@ -48,6 +48,10 @@ This example contains a simple grammar and evaluator for Prolog programs. The co
 dart run bin/prolog/prolog.dart
 ```
 
+### Regular Expressions
+
+This example contains a simple parser and evaluator for regular expressions. It parses patterns, compiles them to Non-deterministic Finite Automata (NFA), and matches them against input text. An interactive playground is provided for the web browser.
+
 ### Smalltalk
 
 This example contains a complete implementation of the Smalltalk grammar. This is a verbatim export of a grammar that was originally developed for the PetitParser infrastructure in Smalltalk and that was the base of the [Helvetia Language Workbench](https://www.lukas-renggli.ch/smalltalk/helvetia).

web/index.html

@@ -33,6 +33,11 @@ <h1>Interactive PetitParser Examples</h1>
             A reasonably complete interpreter that is able to parse and evaluate basic logic programs.
         </dd>
 
+        <dt><a href="regexp/regexp.html">Regular Expression Playground</a></dt>
+        <dd>
+            Parses regular expressions, compiles them to Non-deterministic Finite Automata (NFA), and matches them against input text with interactive visualization.
+        </dd>
+
         <dt><a href="smalltalk/smalltalk.html">Smalltalk Parser</a></dt>
         <dd>
             Contains the beginnings of a Smalltalk Interpreter. Currently only the parsed AST is printed.