docs(intenal/flag_p): adding the documentation of flag_p

includes/_internal.h

@@ -61,6 +61,13 @@ int		flag_c(va_list args, int fd);
  */
 int		flag_i(va_list args, int fd);
 
+/**
+ * @brief Function to handle the flag p in printf's function
+ *
+ * @param args list of arguments
+ * @param fd file descriptor
+ * @return The number of character write in the fd
+ */
 int		flag_p(va_list args, int fd);
 
 int		flag_percent(va_list args, int fd);