Add stub section about the default rounding mode

Closes: #1185

Author: mborland

doc/modules/ROOT/pages/basics.adoc

@@ -96,6 +96,12 @@ int main()
 }
 ----
 
+== Rounding
+
+The default rounding mode for all operations is so-called "banker's rounding", which is to nearest (with ties to even).
+Similar to the standard library, the active rounding mode can be changed through floating point environment variables.
+For more information see: xref:cfenv.adoc[]
+
 == Using the Library
 
 The entire library can be accessed using the convenience header `<boost/decimal.hpp>`.