doc: kernel section title

Change the kernel main title from 'Kernel Services' to the 'The Zephyr
Kernel'

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/doc/kernel/index.rst b/doc/kernel/index.rst
index 032ae2c..c62f0b3 100644
--- a/doc/kernel/index.rst
+++ b/doc/kernel/index.rst
@@ -1,7 +1,7 @@
 .. _kernel_api:
 
-Kernel Services
-###############
+The Zephyr Kernel
+#################
 
 The Zephyr kernel lies at the heart of every Zephyr application. It provides
 a low footprint, high performance, multi-threaded execution environment