Added comments on how streams work

Grbl_Esp32/src/SimpleOutputStream.md

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+# Simple output stream
+
+The simple output stream is a very basic implementation of 
+`std::ostream`, but without all the plumbing and overhead 
+of the std implementation, and without `dynamic_cast`.
+
+The simple output stream is implemented to be able to stream
+data, instead of allocating fixed buffers. For the YAML 
+configuration system, this is mostly useful for streaming 
+data to flash.
+
+The syntax is the same as for std::ostream:
+
+` myStream << "foo" << myInt << etc.;`
+
+**NOTE:** Do NOT use `std::endl` or include `iostream`. Use basic 
+types and strings like `"\n"` instead if needed. 
+
+## Debug stream
+
+`Logging` implements a debug stream, which is basically a way to 
+do (development) logging without creating fixed-size buffers. 
+Currently, the default implementation simply throws the log to
+`Serial`, which should be probably improved at some point to 
+use clients.
+
+Usage:
+
+```c++
+log_info("Twelve is written as " << 12 << ", isn't it");
+```
+
+Available are the following macro's that default to 'void':
+
+- log_debug
+- log_info
+- log_warn
+- log_error
+- log_fatal