purl-validator: Usage documentation for Go

[pombredanne]

The repo is at https://github.com/aboutcode-org/purlvalidator-go

We need a few examples and usage explanations, and what the input should be, especially wrt. versions .... (possibly later with a simple command line wrapper?)

[keshav-space]

This has been completed in aboutcode-org/purlvalidator-go#6 we now show proper error when input is incorrect PURL or if PURL contains unsupported field (version, qualifier and subpath) currently we only support lookup for base PURLs. We also have uses example and examples of various errors in README.