Add link to alumnis LinkedIn group

Author: smelc

README.md

@@ -5,6 +5,9 @@
 This course was/is being given at [Telecom Nancy](https://smelc.github.io/tn-fp-haskell-course/slides/)
 in 2021, 2022, 2023, and 2024 in _3A_.
 
+If you have attended this course, please join the [Telecom Nancy Functional Alumnis](https://www.linkedin.com/groups/13114697/) LinkedIn group 👈
+which I use to post job ads in companies I work with.
+
 ### Online version
 
 Visit [https://smelc.github.io/tn-fp-haskell-course/slides/](https://smelc.github.io/tn-fp-haskell-course/slides/)