Update index.md
Update index.md

restoring commas

Former-commit-id: 4d8e7d1337a65cce3c2db5735a26c5dd5b75bb6f [formerly 656575e2700b971e6a4b3bd4214ab9c1733a225b]
Former-commit-id: d01843271d315fc9982d0013b128e22754fc3c81
LibraryCarpentry/librarycarpentry.github.io,LibraryCarpentry/librarycarpentry.github.io,LibraryCarpentry/librarycarpentry.github.io