Added Sitemap Link to robots.txt
Added Sitemap Link to robots.txt


Former-commit-id: b2207a23064860afb10f04ee269fc68cf9d9edb6 [formerly 4aac4b66a8fd570ac6fbfe5f8afbab6b1a4625c9]
Former-commit-id: e11a9519f2df738853cc30ebdbb4bd0cc30945a3
LibraryCarpentry/librarycarpentry.github.io,LibraryCarpentry/librarycarpentry.github.io,LibraryCarpentry/librarycarpentry.github.io