input: Write a python function to generate an HTML document for a given string solution.
  assert generate_html_doc("def foo(): pass") == "<html>\n<head>\n<title>Python Documentation</title>\n</head>\n<body>\n\n<h1>Solution</h1>\n<pre>\ndef foo(): pass\n</pre>\n\n</body>\n</html>"
  assert generate_html_doc("print('Hello World')") == "<html>\n<head>\n<title>Python Documentation</title>\n</head>\n<body>\n\n<h1>Solution</h1>\n<pre>\nprint('Hello World')\n</pre>\n\n</body>\n</html>"
  assert generate_html_doc("") == "<html>\n<head>\n<title>Python Documentation</title>\n</head>\n<body>\n\n<h1>Solution</h1>\n<pre>\n\n</pre>\n\n</body>\n</html>"
output: def generate_html_doc(solution):
      return f"""<html>
  <head>
  <title>Python Documentation</title>
  </head>
  <body>
  
  <h1>Solution</h1>
  <pre>
  {solution}
  </pre>
  
  </body>
  </html>"""