add(subject): add subject betweenus

subjects/betweenus/README.md

@@ -0,0 +1,36 @@
+## between-us
+
+write a function named `BetweenUs` that takes 3 paramters and checks if the first number is between the second and third number.
+- If the first number is between the second and third number, return `true` else return `false`
+
+### Function
+```go
+func BetweenUs(num, min, max int) bool {
+    // Your code here
+}
+```
+
+
+### Usage
+```go
+package main
+
+import "fmt"
+
+func main(){
+    fmt.Println(BetweenUs(1, 2, 3))
+    fmt.Println(BetweenUs(1, 1, 3))
+    fmt.Println(BetweenUs(1, 3, 3))
+    fmt.Println(BetweenUs(1, 1, 1))
+    fmt.Println(BetweenUs(1, 2, 1))
+}
+```
+
+```console
+$ go run .
+false
+true
+false
+true
+false
+```