website: Add v21.1.0.1 Doxygen link

Change-Id: I0604372b84c3bbff3c5db37e29fd1a9ca5319b05
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/50047
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/_data/documentation.yml b/_data/documentation.yml
index f8a4105..59d3478 100755
--- a/_data/documentation.yml
+++ b/_data/documentation.yml
@@ -48,6 +48,8 @@
           url: http://doxygen.gem5.org/release/v21-0-1-0/index.html
         - page: v21.1.0.0
           url: http://doxygen.gem5.org/release/v21-1-0-0/index.html
+        - page: v21.1.0.1
+          url: http://doxygen.gem5.org/release/v21-1-0-1/index.html
 
     - title: gem5 Resources
       id: gem5_resources