Update instrumentation readme to include links to instrumentation in external repos

[reggiemcdonald]

As per discussion with @MrAlias, we agreed that the readme in the instrumentation directory should be updated to include links to integrations that are not in the opentelemetry-go-contrib repo.

@TigerHe7 and I found that go-redis/go already contains an integration for opentelemetry.

This issue is to update the readme with a table including a link to that repo.

[evantorrie]

I checked https://opentelemetry.io/registry/ and the go-redis/go OTel integration does not appear there either. Should we take it upon ourselves to add this to the registry? Or expect the go-redis maintainers to do so?

[MrAlias]

I checked https://opentelemetry.io/registry/ and the go-redis/go OTel integration does not appear there either. Should we take it upon ourselves to add this to the registry? Or expect the go-redis maintainers to do so?

Probably worth doing ourselves given the newness of things. That said I know @vmihailenco has contributed to OTel already and might be interested in registering it.