website: Fix the layout of CPU models page

Currently, the links to other pages (left pane) does
not show up if you are on the CPU models (index) page.
This change fixes this issue.

Change-Id: Idfb41ab71dc5a5b20e0e5920c8514b27b939c9e7
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/62151
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
diff --git a/_data/documentation.yml b/_data/documentation.yml
index c32e9df..88c021a 100755
--- a/_data/documentation.yml
+++ b/_data/documentation.yml
@@ -155,6 +155,7 @@
 
     - title: CPU Models
       id: cpu_models
+      url: /documentation/general_docs/cpu_models/
       subitems:
         - page: SimpleCPU
           url: /documentation/general_docs/cpu_models/SimpleCPU
diff --git a/_pages/documentation/general_docs/cpu_models/index.md b/_pages/documentation/general_docs/cpu_models/index.md
index 7ebaca3..0ccfec4 100644
--- a/_pages/documentation/general_docs/cpu_models/index.md
+++ b/_pages/documentation/general_docs/cpu_models/index.md
@@ -1,6 +1,8 @@
 ---
 layout: documentation
 title: "gem5's CPU models"
+doc: gem5 documentation
+parent: cpu_models
 permalink: /documentation/general_docs/cpu_models/
 ---