[syserr.errcat.overview] Fixup: notes giving advice to programmers

Author: jensmaurer

source/diagnostics.tex

@@ -845,7 +845,8 @@
 passed by reference, and two such objects
 are equal if they have the same address.
 If there is more than a single object of a custom \tcode{error_category} type,
-such equality comparisons can spuriously fail.
+such equality comparisons can evaluate to \tcode{false}
+even for objects holding the same value.
 \end{note}
 
 \indexlibraryglobal{error_category}%