tinyformat: Add doc to Bitcoin Core specific strprintf

src/tinyformat.h

@@ -1063,6 +1063,7 @@ std::string format(const std::string &fmt, const Args&... args)
 
 } // namespace tinyformat
 
+/** Format arguments and return the string or write to given std::ostream (see tinyformat::format doc for details) */
 #define strprintf tfm::format
 
 #endif // TINYFORMAT_H_INCLUDED