feat:Add The Countchar subject

subjects/count-character/README.md

@@ -0,0 +1,44 @@
+# count-character
+
+### Instructions
+write a function that takes a string and a character as arguments and returns the number of times the character appears in the string
+  
+    if the character is not in the string return 0
+    if the string is empty return 0
+
+### Expected Function
+
+```go
+    func CountChar(str string, c rune) int {
+        ...
+    }
+```
+
+### Usage
+
+```go
+    package main
+
+    import (   
+        "fmt"
+        "piscine"
+    )
+
+    func main() {
+        fmt.Println(CountChar("Hello World", 'l'))
+        fmt.Println(CountChar("5  balloons",5))
+        fmt.Println(CountChar("   ", ' '))
+        fmt.Println(CountChar("The deadly 7 sins", '7'))
+    }
+```
+
+And its output :
+
+```console
+    $ go run .
+    3
+    0
+    1
+    1
+```
+