Update README.md to warn about possible network failures in call to SerialKey.Set

[eulerfx]

Added a warning for network failures in the call to SerialKey.Set

It would be nice if the operation returned a Task rather than void to indicate that network IO is taking place. In cloud environments, there may be transient DNS issues which are handled by retry policies. I'd recommend accepting an IHttpClientFactory or making the HttpClient configurable in some other way.

Regardless, users should be aware of this potential point of failure and be prepared to apply retry policies (which make the application a lot more complicated).