Improve pkg-config integration a bit

CMake/catch2.pc.in

@@ -1,6 +1,7 @@
 includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@
 
 Name: Catch2
-Description: Testing library for C++
+Description: A modern, C++-native, header-only, test framework for C++11
+URL: https://github.com/catchorg/Catch2
 Version: @Catch2_VERSION@
 Cflags: -I${includedir}