website: Add link to v21.2.1.1 Doxygen link

Change-Id: I620ed9e85aadb23a8e912841b8ed2baa56e58e05
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/59353
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
diff --git a/_data/documentation.yml b/_data/documentation.yml
index 33cfcc7..215a320 100755
--- a/_data/documentation.yml
+++ b/_data/documentation.yml
@@ -56,6 +56,8 @@
           url: http://doxygen.gem5.org/release/v21-2-0-0/index.html
         - page: v21.2.1.0
           url: http://doxygen.gem5.org/release/v21-2-1-0/index.html
+        - page: v21.2.1.1
+          url: http://doxygen.gem5.org/release/v21-2-1-1/index.html
 
     - title: gem5 standard library
       id: gem5-standard-library