Add Readme as documentation entry

docs/Readme.md

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+These are the currently documented areas of the framework. There is more to come.
+
+Before looking at this material be sure to read the [tutorial](tutorial.md)
+
+* [Assertion macros](assertions.md)
+* [Logging macros](logging.md)
+* [Test cases and sections](test-cases-and-sections.md)
+* [Test fixtures](test-fixtures.md)
+* [Command line](command-line.md)
+* [Build systems](build-systems.md)
+* [Supplying your own main()](own-main.md)
+* [Why are my tests slow to compile?](slow-compiles.md)
+
+Other
+
+* [Why Catch?](why-catch.md)
+* [What's changed](whats-changed.md)
+* [Contributing](contributing.md)
+
+---
+
+[Home](../README.md)
+