Added "How to test changes in PR" section to documentation

Also linked it from PR template.

Closes #936

.github/pull_request_template.md

@@ -2,6 +2,9 @@
 Please do not submit pull requests changing the `version.hpp`
 or the single-include `catch.hpp` file, these are changed
 only when a new release is made.
+
+Before submitting a PR you should probably read the contributor documentation
+at docs/contributing.md. It will tell you how to properly test your changes.
 -->
 
 

docs/contributing.md

@@ -18,8 +18,8 @@ Ongoing development is currently on _master_. At some point an integration branc
 _Users_ of Catch primarily use the single header version. _Maintainers_ should work with the full source (which is still, 
 primarily, in headers). This can be found in the `include` folder. There are a set of test files, currently under
 `projects/SelfTest`. The test app can be built via CMake from the `CMakeLists.txt` file in the root, or you can generate
-project files for Visual Studio, XCode, and others (instructions in the `projects` folder). If you have access to CLion
-that can work with the CMake file directly.
+project files for Visual Studio, XCode, and others (instructions in the `projects` folder). If you have access to CLion,
+it can work with the CMake file directly.
 
 As well as the runtime test files you'll also see a `SurrogateCpps` directory under `projects/SelfTest`.
 This contains a set of .cpp files that each `#include` a single header.
@@ -34,6 +34,25 @@ __When submitting a pull request please do not include changes to the single inc
 as these are managed by the scripts!__
 
 
+## Testing your changes
+
+Obviously all changes to Catch's code should be tested. If you added new functionality, you should add tests covering and
+showcasing it. Even if you have only made changes to Catch internals (ie you implemented some performance improvements),
+you should still test your changes.
+
+This means 3 things
+
+* Compiling Catch's SelfTest project -- code that does not compile is evidently incorrect. Obviously, you are not expected to
+have access to all compilers and platforms Catch supports, Catch's CI pipeline will compile your code using supported compilers
+once you open a PR.
+* Running the SelfTest binary. There should be no unexpected failures on simple run.
+* Running Catch's approval tests. Approval tests compare current output of the SelfTest binary in various configurations against
+known good output. Catch's repository provides utility scripts `approvalTests.py` to help you with this. It needs to be passed
+the SelfTest binary compiled with your changes, like so: `$ ./scripts/approvalTests.py clang-build/SelfTest`. The output should
+be fairly self-explanatory.
+
+
+
  *this document is still in-progress...*
 
 ---