Update 'backlog.md'

backlog.md

@@ -69,6 +69,7 @@
 - [Blumberg Theorem](https://en.wikipedia.org/wiki/Blumberg_theorem)
 - [Central Limit Theorem](https://en.wikipedia.org/wiki/Central_limit_theorem)
 - [Gershgorin circle theorem](https://en.wikipedia.org/wiki/Gershgorin_circle_theorem)
+- [Science as a Vocation](https://en.wikipedia.org/wiki/Science_as_a_Vocation)
 
 ## Reference Book Backlog
 - Bartlett's Familiar Quotations