Add credits to Anagram Crossword.

www/crossword/index.html

@@ -369,6 +369,19 @@
         leaving spaces blank. Note that empty spaces can be frozen to make
         this easier.
       </p>
+
+      <h2>Credits</h2>
+      <ul>
+        <li>Game design cloned from iOS game <a href="https://itunes.apple.com/us/app/wordscapes/id1207472156">Wordscapes</a></li>
+        <li>Common words list from <a href="https://github.com/hermitdave/FrequencyWords">FrequencyWords</a> (see its credits and license at that link)</li>
+        <li>Valid word checks (spellchecking) using <a href="https://github.com/cfinke/Typo.js">Typo.js</a> (see its credits and license at that link)</li>
+        <li>Programming by <a href="https://aweirdimagination.net/~perelman/">Daniel Perelman</a>, licensed <a href="https://www.gnu.org/licenses/agpl-3.0.en.html">AGPLv3+</a></li>
+        <ul>
+          <li><a href="https://git.aweirdimagination.net/perelman/anagram-games/src/branch/master">Source code git repository</a></li>
+          <li>See also: <a href="https://aweirdimagination.net/tag/anagram-crossword/">blog posts about this game</a></li>
+        </ul>
+      </ul>
+
     </div>
     <table id="crossword">
     </table>