docs: fix broken links in landing page

Updated the URL for the SPM documentation.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I35f386a78620888ace3f83b065f28f6f9bfecfce
diff --git a/readme.rst b/readme.rst
index 4fcd492..54724b8 100644
--- a/readme.rst
+++ b/readme.rst
@@ -60,7 +60,7 @@
 
 .. _Firmware update: https://trustedfirmware-a.readthedocs.io/en/latest/components/firmware-update.html
 .. _EL3 payload: https://trustedfirmware-a.readthedocs.io/en/latest/design/alt-boot-flows.html#el3-payloads-alternative-boot-flow
-.. _Secure partition: https://trustedfirmware-a.readthedocs.io/en/latest/components/secure-partition-manager-design.html
+.. _Secure partition: https://trustedfirmware-a.readthedocs.io/en/latest/components/secure-partition-manager.html
 
 .. _view the full documentation: https://trustedfirmware-a-tests.readthedocs.io/
 .. _trustedfirmware.org: http://www.trustedfirmware.org