Document the io.l5d.mesh interface private key format (#1359)
Document the io.l5d.mesh interface private key format (#1359)

Problem

Unlike the `io.l5d.namerd` and `io.l5d.namerd.http` interfaces, namerd's
`io.l5d.mesh` interface cannot be configured with a PKCS#1 private key.
This is due to the interface using netty4 to server gRPC requests.

Solution

Specify the format of the key that's required as part of the
`io.l5d.mesh` interface documentation.
BuoyantIO/linkerd,denverwilliams/linkerd,denverwilliams/linkerd,denverwilliams/linkerd,linkerd/linkerd,denverwilliams/linkerd,BuoyantIO/linkerd,linkerd/linkerd,linkerd/linkerd