add an example with `/` in namespace to README and SPEC

[maxhbr]

I think it is not clear from the text in the README and the examples whether a / in the namespace needs to be escaped. This adds an example from /test-suite-data.json to the list of examples, to make that clear, that escaping should not be done.

A follow-up question, that is not scope of this PR, would be:

given the PURL pkg:swift/github.com%2FAlamofire/[email protected] is pkg:swift/github.com/Alamofire/[email protected] its canonical form? If yes, it should be added to the test cases.

Or, for having more fun and with looking at #63 : what is the canonical form of pkg:golang/github.com%2Frussross%2Fblackfriday%[email protected]?