Minor addition.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@1645 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/helgrind/docs/hg_main.html b/helgrind/docs/hg_main.html
index cb88cae..99f56da 100644
--- a/helgrind/docs/hg_main.html
+++ b/helgrind/docs/hg_main.html
@@ -45,11 +45,15 @@
 protect that location.  If no such lock can be found, then there is 
 (apparently) no consistent locking strategy being applied for that
 location, and so a possible data race might result.
-
+<p>
+Helgrind also allows for "thread segment lifetimes".  If the execution of two
+threads cannot overlap -- for example, if your main thread waits on another
+thread with a <code>pthread_join()</code> operation -- they can both access the
+same variable without holding a lock.
 <p>
 There's a lot of other sophistication in the Helgrind skin, aimed at
 reducing the number of false reports, and at producing useful error
-reports.  We hope to have more documentation soon.
+reports.  We hope to have more documentation one day...
 
 </body>
 </html>