Added note about the test file formatting

CONTRIBUTING.md

@@ -1,3 +1,24 @@
 # Contribution guide
 
 The code is formatted using the K&R style of "indent".
+
+```
+indent -kr <files go here>
+```
+
+The C unit tests have also been indented in the same way, but manually adjsted
+such that the functions follow the normal libcheck layout.
+
+```c
+START_TEST( ... ) {
+
+
+}
+END TEST
+```
+
+Indent tends to mangle the `END_TEST` macro, so that will need adjusting if
+`indent` is run over the test files again.
+
+
+