Update front page warning

Author: MetRonnie

src/release-note.rst

@@ -1,6 +1,6 @@
 .. note::
 
-   Cylc |release| is the final *beta* pre-release of Cylc 8. It is largely
+   Cylc |release| is a Cylc 8 *release candidate*. It is largely
    complete and can be used to manage real workflows, but it has not yet been
    heavily tested by users. Python 2 based Cylc 7 is stable and still available
    if needed for production systems.