Add readable books as a special item ability

doc/editor/appendix/Items.html

@@ -363,6 +363,12 @@ Item Adjust setting is ignored.</dd>
 <dt>Ability 84 - Quickfire</dt>
 <dd>Creates quickfire on space where its used. The Magic Item Adjust setting is ignored, as
 are the extra data fields..</dd>
+<dt>Ability 85 - Book</dt>
+<dd>The item is a book which gives some textual information when used. A book does not
+consume any charges when used. To set the contents of the book, edit the item description.
+At the end of the description, add three vertical bars (<pre>|</pre>) followed by the
+content of the book. If you want, you can add another three vertical bars followed by a
+second string. Note that there is limited space for the strings in the dialog.</dd>
 </dl>
 
 <h2 id='reagent'>Reagents (Inherent)</h2>