Once g-c-j supports Java 11, add note that g-c-j can be used on Alpine and ARM (e.g. Raspberry Pi)

[garrettjonesgoogle]

Reason: ALPN is available by default in Java 11, so netty-tcnative is not necessary.

[chingor13]

We are only declaring a dependencyManagement version on netty-tcnative, but it's not actually in the dependency tree. We're using io.grpc:grpc-netty-shaded which includes netty-tcnative.

[garrettjonesgoogle]

Both grpc-netty and grpc-netty-shaded don't work on Alpine or ARM. I'm kind of treating grpc-netty/grpc-netty-shaded as equivalent for this issue; the point is that I think neither one of them is strictly necessary in the dependency tree with Java 11, because ALPN is available by default in Java 11, meaning that grpc & google-cloud-java should work on Alpine and ARM in Java 11.

[sduskis]

Would it make sense to mark this as a "feature request" rather than "docs"? It seems like we have work to do before we document anything.

[jbg]

Works well on Alpine Linux here with Java 11. (Does not work with Java 8 due to netty-tcnative incompatibility.)