Better instructions for installing Catch 2. Catch 3 is not supported.

Author: DavidEGrayson

test/CMakeLists.txt

@@ -1,9 +1,8 @@
 INCLUDE (CheckIncludeFileCXX)
 
-# If catch.hpp is not present, we want to simply skip compiling the tests.  This
-# allows someone to compile and install libusbp without having catch installed.
-# The header can either be installed in this directory or in a standard system
-# location.
+# If catch.hpp is not present, we want to simply skip compiling the tests.
+# Download catch.hpp and put it in this directory:
+# https://raw.githubusercontent.com/catchorg/Catch2/v2.x/single_include/catch2/catch.hpp
 set (CMAKE_REQUIRED_INCLUDES "${CMAKE_CURRENT_SOURCE_DIR}")
 CHECK_INCLUDE_FILE_CXX (catch.hpp HAVE_CATCH_FRAMEWORK)
 if (NOT HAVE_CATCH_FRAMEWORK)