mention C11 in case someone wonders

src/atomics.md

@@ -6,6 +6,9 @@ this model is quite complex and known to have [several flaws][C11-busted].
 Rather, it is a pragmatic concession to the fact that *everyone* is pretty bad
 at modeling atomics. At very least, we can benefit from existing tooling and
 research around the C/C++ memory model.
+(You'll often see this model referred to as "C11" or "C/C++11". C and C++ share their
+memory model and those were the first versions but they have received some bugfixes
+since then.)
 
 Trying to fully explain the model in this book is fairly hopeless. It's defined
 in terms of madness-inducing causality graphs that require a full book to