Add an example to fmt::runtime

include/fmt/core.h

@@ -2956,7 +2956,16 @@ template <typename S> auto runtime(const S& s) -> basic_string_view<char_t<S>> {
 #else
 template <typename... Args>
 using format_string = basic_format_string<char, type_identity_t<Args>...>;
-/** Creates a runtime format string. */
+/**
+  \rst
+  Creates a runtime format string.
+
+  **Example**::
+
+    // Check format string at runtime instead of compile-time.
+    fmt::print(fmt::runtime("{:d}"), "I am not a number");
+  \endrst
+ */
 template <typename S> auto runtime(const S& s) -> basic_runtime<char_t<S>> {
   return {{s}};
 }