website: Add v21.0.1.0 Doxygen link

Change-Id: I0a7e4aca6100179b7a4831c8412e55339f9274e3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/47139
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 9ae3d00..e531391 100755
--- a/_data/documentation.yml
+++ b/_data/documentation.yml
@@ -40,6 +40,8 @@
           url: http://doxygen.gem5.org/release/v20-1-0-5/index.html
         - page: v21.0.0.0
           url: http://doxygen.gem5.org/release/v21-0-0-0/index.html
+        - page: v21.0.1.0
+          url: http://doxygen.gem5.org/release/v21-0-1-0/index.html
 
     - title: gem5 Resources
       id: gem5_resources