JCF: reverting back to the C++17 standard for now since the compiler …

…flags in

daq-cmake assume C++17

Revert "JCF: express support for C++20 standard"

This reverts commit 2d7288c.

docs/README.md

@@ -109,7 +109,8 @@ familiar with the language.
 
 ## 1.  C++ Version 
 
-Currently, code should target C++20
+Currently, code should target C++17, i.e., should not use C++2x
+features.
 
 ## 2. Naming Conventions