Update docs

doc/api.rst

@@ -493,7 +493,9 @@ System APIs
 ========================
 
 ``fmt/ostream.h`` provides ``std::ostream`` support including formatting of
-user-defined types that have an overloaded insertion operator (``operator<<``)::
+user-defined types that have an overloaded insertion operator (``operator<<``).
+In order to make a type formattable via ``std::ostream`` you should provide a
+``formatter`` specialization inherited from ``ostream_formatter``:
 
   #include <fmt/ostream.h>
 
@@ -507,14 +509,11 @@ user-defined types that have an overloaded insertion operator (``operator<<``)::
     }
   };
 
-  template <> struct fmt::formatter<date> : ostream_formatter<date> {};
+  template <> struct fmt::formatter<date> : ostream_formatter {};
 
   std::string s = fmt::format("The date is {}", date(2012, 12, 9));
   // s == "The date is 2012-12-9"
 
-{fmt} only supports insertion operators that are defined in the same namespaces
-as the types they format and can be found with the argument-dependent lookup.
-
 .. doxygenfunction:: print(std::basic_ostream<Char> &os, const S &format_str, Args&&... args)
 
 .. _printf-api: