package/fmt: add an upstream URL to Config.in

Add an upstream URL to the help text in Config.in. This
addresses the 'Missing' URL status in the package stats
web page output.

Signed-off-by: Mark Corbin <mark@dibsco.co.uk>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/fmt/Config.in

@@ -7,5 +7,7 @@ config BR2_PACKAGE_FMT
 	  used as a safe alternative to printf or as a fast alternative
 	  to IOStreams.
 
+	  https://fmt.dev
+
 comment "fmt needs a toolchain w/ C++, wchar"
 	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_USE_WCHAR