Add 'on to' to the list of compound words not to modernize

www/contribute/how-tos/things-to-look-out-for-when-proofreading.php

@@ -18,6 +18,7 @@
 				<li><p><br>Compound words.</b> Some words that today are usually written as a single word may in older works be printed as two words separated by a space or a hyphen. The most common cases are handled by <code class="bash"><b>se</b> modernize-spelling</code>, however there are so many possible combinations that eliminating or standardizing all of them would be a major challenge. As such it is <i>not required</i> to change compound words, although this can <i>optionally</i> be done provided there is sufficient evidence that a modern printing would do so. The following words are exceptions and <i>should never be modernized</i> (<abbr class="initialism">N.B. this does not mean we split them if they are already printed as a single word):</p>
 				<ul>
 						<li><p>none the less</p></li>
+				        <li><p>on to</p></li>
 						<li><p>worth while</p></li>
 				</ul>
 				</li>