docs(readme): fix gRPC example

[bastianccm]

tldr: envoy uses nghttp2, which reports invalid frame: Violation in HTTP messaging rule on stream 1

Long Story: If you use this example in a server node.js process in Kubernetes with an Istio Service Mesh, envoy will report something like

│ 2022-08-29T12:53:55.616404Z    debug    envoy http2    [C398] updating connection-level initial window size to 268435456                                                                                                                                                                                                   │
│ 2022-08-29T12:53:55.616663Z    debug    envoy http2    [C398] invalid frame: Violation in HTTP messaging rule on stream 1

if you try to call an gRPC request. Sadly, there is basically no documentation at all available for this behaviour.
The Promise will reject with Connection dropped and no other details.
Prepending the / to the path ensures that the behaviour is not violating the HTTP/2 standard, because appearently node http2 package does allow the path to not start with /.
See https://www.rfc-editor.org/rfc/rfc7540#section-8.1.2 8.1.2.3 and https://www.rfc-editor.org/rfc/rfc3986#section-3.3

The ":path" pseudo-header field includes the path and query parts of the target URI (the "path-absolute" [...]

If you develop locally against a different gRPC server, such as the go grpc implementation, this error does not occur, go will accept the missing / and simply work.

Thank you for this great project, really appreciate your work!

[stephenh]

Ah wow, yeah that looks cryptic @bastianccm ; thanks for the update!

[stephenh]

🎉 This PR is included in version 1.124.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release
• v1.124.0

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