Custom Report Labels

- Added the ability to override the labels of custom reports (thanks
  to T. Charles Yun).

html/custom.html

@@ -88,6 +88,18 @@ report.mine.sort=priority-,project+</pre></code>
                   in a report:
                 </p>
 
+                <p>
+                  It is also possible to override the default columns names, if
+                  the following line is added to your .taskrc file:
+                </p>
+
+                <pre><code>report.mine.labels=ID,Project,Priority,Description of task</code></pre>
+
+                <p>
+                  Note that there must be the same number of labels as there are
+                  columns to label, and they must appear in the same sequence.
+                </p>
+
                 <ul>
                   <li>id
                   <li>uuid