Add example showing the except functions

[heueristik]

Currently, we only show how to use the assert functions

juvix-test/README.md

Lines 9 to 30 in 3103c41

	```
	module Example;
	import Stdlib.Prelude open;
	import Test.JuvixUnit open;
	tests : List Test :=
	[testCase "1 == 1" (assertEqual "1 /= 1" 1 1)];
	main : IO := runTestSuite (testSuite "Example" tests);
	```
	Compile and run the test suite:
	``` shell
	$ juvix compile Example.juvix
	$ ./Example
	Test suite 'Example'
	1 == 1 OK
	All tests from test suite 'Example' complete
	Suite passed
	```

but not how to use the except functions.