Update README.md

Author: lucadegasperi

README.md

@@ -19,6 +19,7 @@ The package assumes you have a good-enough knowledge of the principles behind th
  4.1.x    | 1.0.x        |>= 5.3
  4.2.x    | 3.0.x        |>= 5.4
  5.0.x    | 4.0.x        |>= 5.4
+ 5.1.x    | 4.1.x        |>= 5.5
 
 ## Documentation