ref-manual: New section clarifying stamps, input checksums and sstate cache

Fixes [YOCTO #10172]

I added a new section on how BitBake reruns tasks based on the
stamps files.  Also put in some cross-referencing links to that
new section in the stamps entry for the structure chapter and in
the STAMP variable in the glossary.

(From yocto-docs rev: da8779d9eb85473cd6b0f74e9e1371e1d277890f)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/ref-manual/ref-structure.xml

@@ -801,8 +801,9 @@
         <title><filename>build/tmp/stamps/</filename></title>
 
         <para>
-            This directory holds information that BitBake uses for accounting purposes
-            to track what tasks have run and when they have run.
+            This directory holds information that BitBake uses for
+            accounting purposes to track what tasks have run and when they
+            have run.
             The directory is sub-divided by architecture, package name, and
             version.
             Following is an example:
@@ -812,6 +813,13 @@
             Although the files in the directory are empty of data,
             BitBake uses the filenames and timestamps for tracking purposes.
         </para>
+
+        <para>
+            For information on how BitBake uses stamp files to determine if
+            a task should be rerun, see the
+            "<link linkend='stamp-files-and-the-rerunning-of-tasks'>Stamp Files and the Rerunning of Tasks</link>"
+            section.
+        </para>
     </section>
 
     <section id='structure-build-tmp-log'>