sync up Jekyll based website with PHP one

[rhaas80]

We need to find changes to the PHP based site since the Jekyll one was spun off in a135947 on Tue Feb 11 16:48:10 2020 +0000 ie:

git log --since "Tue Feb 11 16:48:10 2020 +0000"

which thankfully amounts to:

$ git log --since "Tue Feb 11 16:48:10 2020 +0000"
commit b5c5201653640c25f098d9402772ed389dd0dd3f (HEAD -> master)
Author: Roland Haas <rhaas@illinois.edu>
Date:   Sun May 31 14:26:43 2020 +0000

    add ET_2020_05 release and Cactus 4.8.0

commit d82782793779498b5b3f90e474b6a05d70373f73
Author: Roland Haas <rhaas@illinois.edu>
Date:   Sun May 31 14:10:08 2020 +0000

    correct Cactus 4.7.0 text, add ET_2020_05 text

[rhaas80]

Updated in 323a67c to revision 492 (current trunk of https://svn.cactuscode.org/www/).