Add CMake example

cmake-example/vendor/Catch2/CMakeLists.txt

@@ -0,0 +1,7 @@
+# Since we bring along our own version of Catch2, we prefix the target with the
+# project name. Alternatively we could check whether Catch2::Catch2 is already
+# available and use that one instead of our own via `add_library(mylib_Catch2
+# ALIAS Catch2::Catch2)`.
+
+add_library(mylib_Catch2 INTERFACE)
+target_include_directories(mylib_Catch2 INTERFACE .)