Update RGBDS master documentation

Author: GitHub Action

docs/gbz80.7.pdf

@@ -1082,8 +1082,9 @@ <h3 class="Ss" id="Other_functions"><a class="permalink" href="#Other_functions"
     <td>If <var class="Ar">arg</var> is a string, this function returns the size
       of the section named <var class="Ar">arg</var>. If
       <var class="Ar">arg</var> is a section type keyword, it returns the size
-      of that section type. The result is not constant, since only RGBLINK can
-      compute its value.</td>
+      of that section type. If <var class="Ar">arg</var> is an 8-bit or 16-bit
+      register, it returns the size of that register. The result is not
+      constant, since only RGBLINK can compute its value.</td>
   </tr>
   <tr id="STARTOF">
     <td><a class="permalink" href="#STARTOF"><code class="Fn">STARTOF</code></a>(<var class="Fa">arg</var>)</td>