Explain correct situation too

Author: amirhasanpour

content/chapter 6/6.7-limitations, errors, and anti-patterns in generics.md

@@ -59,13 +59,23 @@ weight: 11007
 #### مثال واقعی خطا:
 
 ```go
+package main
+
+import "fmt"
+
 func PrintMapKeys[K comparable, V any](m map[K]V) {
-    for k := range m {
-        fmt.Println(k)
-    }
+	for k := range m {
+		fmt.Println(k)
+	}
 }
 
-PrintMapKeys(map[[]int]int{}) // error: []int does not implement comparable
+func main() {
+	PrintMapKeys(map[[]int]int{}) // error: []int does not implement comparable
+
+	// use this instead:
+	// testMap := make(map[string]int)
+	// PrintMapKeys(testMap)
+}
 ```
 
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