Update docs yet again

Author: ckormanyos

README.md

@@ -238,12 +238,9 @@ and their directly relevant code sequences have been removed.
 Simple mechanisms such as those found in `<cassert>`
 and `<cerrno>`, however, remain mostly available.
 
-- **`<atomic>`:** Even though the intended compilers are built with no threading,
-the `<atomic>` library and its use as a dependency has
-been removed. This means that atomic functions and
-atomic store/load functions are not available. So if you are sharing
-data in an operating system or mixed program/interrupt mode,
-self-written atomic primitives are needed.
+- **`<atomic>`:** The `<atomic>` library is being handled
+specifically in the draft of
+[avr-libstdcpp/pull/36](https://github.com/modm-io/avr-libstdcpp/pull/36).
 
 - **`<random>`:** There is no source of entropy whatsoever on these platforms
 in their standard configuration. So `std::random_device`
@@ -331,18 +328,24 @@ int main()
 ```
 
 See also the [numeric.cpp](./examples/numeric/numeric.cpp) file
-in the [./examples/numeric](./examples/numeric) directory.
+in the [/examples/numeric](./examples/numeric) directory.
 
 ## Additional details
 
 `avr-libstdcpp` is intended for a modern `avr-gcc`
 such as the port available in the [modm-io project](https://github.com/modm-io/avr-gcc)
-repository. Tests show usability also for `avr-gcc` 7 through 14 (and beyond).
+repository. Tests show usability for `avr-gcc` 7 through 15.
 
-Using the port way back to `avr-gcc` 5, however, does not work
+This library has been checked for compatibility on `avr-gcc`
+with language standards C++11,14,17,20,23 and 2c.
+
+Using the port way back to `avr-gcc` 5 does not work
 at the moment with today's form of the checked-in library,
-as the older compiler's lexical parser is not capable of
-properly handling some of the library's template code.
+and `avr-gcc` 7 or higher is required.
+This is because the very old compiler lexical parsers are not capable
+of properly handling some of the library's template code.
+See also [avr-libstdcpp/issues/15](https://github.com/modm-io/avr-libstdcpp/issues/15)
+which is closed and includes justification for its closure.
 
 ## Licensing