Improve documentation about using Catch with CMake

Also added a note about the `contrib/ParseAndAddCatchTests.cmake`
script.

Closes #882

docs/build-systems.md

@@ -56,8 +56,26 @@ Because of the incremental nature of Catch's test suites and ability to run spec
 
 ## CMake
 
-You can use the following CMake script to automatically fetch Catch from github and configure it as an external project:
+In general we recommend "vendoring" Catch's single-include releases inside your own repository. If you do this, the following example shows a minimal CMake project:
+```CMake
+cmake_minimum_required(VERSION 3.0)
+
+project(cmake_test)
+
+# Prepare "Catch" library for other executables
+set(CATCH_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/catch)
+add_library(Catch INTERFACE)
+target_include_directories(Catch INTERFACE ${CATCH_INCLUDE_DIR})
+
+# Make test executable
+set(TEST_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/main.cpp)
+add_executable(tests ${TEST_SOURCES})
+target_link_libraries(tests Catch)
+```
+Note that it assumes that the path to the Catch's header is `catch/catch.hpp` from the `CMakeLists.txt` file.
+
 
+You can also use the following CMake snippet to automatically fetch the entire Catch repository from github and configure it as an external project:
 ```CMake
 cmake_minimum_required(VERSION 2.8.8)
 project(catch_builder CXX)
@@ -90,6 +108,32 @@ include_directories(${CATCH_INCLUDE_DIR} ${COMMON_INCLUDES})
 enable_testing(true)  # Enables unit-testing.
 ```
 
+The advantage of this approach is that you can always automatically update Catch to the latest release. The disadvantage is that it means bringing in lot more than you need.
+
+
+### Automatic test registration
+If you are also using ctest, `contrib/ParseAndAddCatchTests.cmake` is a CMake script that attempts to parse your test files and automatically register all test cases, using tags as labels. This means that these
+```cpp
+TEST_CASE("Test1", "[unit]") {
+    int a = 1;
+    int b = 2;
+    REQUIRE(a == b);
+}
+
+TEST_CASE("Test2") {
+    int a = 1;
+    int b = 2;
+    REQUIRE(a == b);
+}
+
+TEST_CASE("Test3", "[a][b][c]") {
+    int a = 1;
+    int b = 2;
+    REQUIRE(a == b);
+}
+```
+would be registered as 3 tests, `Test1`, `Test2` and `Test3`, and ctest 4 labels would be created, `a`, `b`, `c` and `unit`.
+
 ---
 
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