vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc/README.md

@@ -0,0 +1,57 @@
+# OpenTracing support for gRPC in Go
+
+The `otgrpc` package makes it easy to add OpenTracing support to gRPC-based
+systems in Go.
+
+## Installation
+
+```
+go get github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc
+```
+
+## Documentation
+
+See the basic usage examples below and the [package documentation on
+godoc.org](https://godoc.org/github.com/grpc-ecosystem/grpc-opentracing/go/otgrpc).
+
+## Client-side usage example
+
+Wherever you call `grpc.Dial`:
+
+```go
+// You must have some sort of OpenTracing Tracer instance on hand.
+var tracer opentracing.Tracer = ...
+...
+
+// Set up a connection to the server peer.
+conn, err := grpc.Dial(
+    address,
+    ... // other options
+    grpc.WithUnaryInterceptor(
+        otgrpc.OpenTracingClientInterceptor(tracer)),
+    grpc.WithStreamInterceptor(
+        otgrpc.OpenTracingStreamClientInterceptor(tracer)))
+
+// All future RPC activity involving `conn` will be automatically traced.
+```
+
+## Server-side usage example
+
+Wherever you call `grpc.NewServer`:
+
+```go
+// You must have some sort of OpenTracing Tracer instance on hand.
+var tracer opentracing.Tracer = ...
+...
+
+// Initialize the gRPC server.
+s := grpc.NewServer(
+    ... // other options
+    grpc.UnaryInterceptor(
+        otgrpc.OpenTracingServerInterceptor(tracer)),
+    grpc.StreamInterceptor(
+        otgrpc.OpenTracingStreamServerInterceptor(tracer)))
+
+// All future RPC activity involving `s` will be automatically traced.
+```
+