Expanded the practical example in slow-compiles documentation

docs/slow-compiles.md

@@ -42,6 +42,21 @@ TEST_CASE( "Factorials are computed", "[factorial]" ) {
 
 After compiling `tests-main.cpp` once, it is enough to link it with separately compiled `tests-factorial.cpp`. This means that adding more tests to `tests-factorial.cpp`, will not result in recompiling Catch's main and the resulting compilation times will decrease substantially.
 
+```
+$ g++ tests-main.cpp -c
+$ g++ tests-main.o tests-factorial.cpp -o tests && ./tests -r compact
+Passed 1 test case with 4 assertions.
+```
+
+Now, the next time we change the file `tests-factorial.cpp` (say we add `REQUIRE( Factorial(0) == 1)`), it is enough to recompile the tests instead of recompiling main as well:
+
+```
+$ g++ tests-main.o tests-factorial.cpp -o tests
+$ g++ tests-main.o tests-factorial.cpp -o tests && ./tests -r compact
+tests-factorial.cpp:11: failed: Factorial(0) == 1 for: 0 == 1
+Failed 1 test case, failed 1 assertion.
+```
+
 
 ---