Introduce specification APPENDICES

These are advisory tests implementations optionally may
choose to follow. Provides the space for tests that are more broad
than implementation-specific tests, yet might not be something
we mandate all implementations must follow (e.g. overflow tests)

APPENDICES/README.md

@@ -0,0 +1,28 @@
+# Perl 6 Specification Appendices
+
+The `APPENDICES` directory of the Perl 6 specification contains *advisory*
+specifications. These tests describe behaviour some implementations chose
+to follow and other implementations may follow the same behaviour, to offer
+similar execution results from same Perl 6 programs.
+
+However, it's possible some implementations or some environments may not
+be able to adhere to these specifications. For example, an implementation
+that can compute `2**-10000000000` sufficiently fast may choose to use
+higher limits for powers before throwing overlow exceptions.
+
+In summation, the APPENDICES contain tests that fall somewhere between
+implementation-specific tests residing in test suites of particular
+implementations and regular specification tests that all implementations
+must adhere to.
+
+An implementation may fail all of the tests in APPENDICES, yet still claim
+the status of being a fully-compliant Perl 6 implementation.
+
+## Available Appendices
+
+### [`A01-limits`](A01-limits)
+
+Contains tests of potentially-desirable behaviour that's dependent on the
+limitations of typical environments. For example, raising a number to a
+huge power effectively "hangs" the program, so the tests check such cases
+throw an overflow error instead.

README.md

@@ -139,6 +139,12 @@ Depending on the location of your test file, the number inside `.parent(2)`
 may need to be adjusted to go up the correct number of times from the test
 files's location to the root of the repository.
 
+## Appendices
+
+The [`APPENDICES`](APPENDICES/) directory contains advisory tests implentations
+may optionally choose to follow. See the [`README`](APPENDICES/README.md)
+included in that directory for more information.
+
 ## Environmental Variables
 
 - **ROAST_TIMING_SCALE**