chore(readme): update readme

README.md

@@ -55,10 +55,25 @@ int vsnprintf(char* buffer, size_t count, const char* format, va_list va);
 int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...);
 ```
 
-
 **Due to genaral security reasons it is highly recommended to prefer and use `snprintf` (with the max buffer size as `count` parameter) instead of `sprintf`.**  
 `sprintf` has no buffer limitation, so when needed - use it really with care!
 
+### Streamlike usage
+Besides the regular standard `printf()` functions, this module also provides `fctprintf()`, which takes an output function as first parameter to build a streamlike output like `fprintf()`:
+```C
+// define the output function
+void my_stream_output(char character, void* arg)
+{
+  // opt. evaluate the argument and send the char somewhere
+}
+
+{
+  // in your code
+  void* arg = (void*)100;  // this argument is passed to the output function
+  fctprintf(&my_stream_output, arg, "This is a test: %X", 0xAA);
+  fctprintf(&my_stream_output, nullptr, "Send to null dev");
+}
+```
 
 ## Format specifiers