docs(example): add a simple example to test google-pubsub

examples/google-pubsub/README.md

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+# PubSub Example: Google Cloud Pub/Sub
+
+Sample Express application in order to test the @algoan/pubsub library with Google Pub/Sub.
+
+## Getting Started
+
+Install dependencies:
+
+```shell
+npm i
+```
+
+Run a google Pub/Sub emulator using gcloud CLI. You must ensure that `beta` and `pubsub-emulator` are installed:
+
+```shell
+gcloud components install pubsub-emulator
+gcloud components install beta
+gcloud components update
+````
+
+You can also run the emulator using Docker:
+
+```shell
+docker pull google/cloud-sdk:emulators
+docker run --rm -p 8085:8085 google/cloud-sdk:emulators /bin/bash -c "gcloud beta emulators pubsub start --project=test --host-port='0.0.0.0:8085'"  
+```
+
+Then, run:
+
+```shell
+npm start
+```
+
+Navigate on http://localhost:3000! To emit an event, simply call GET http://localhost:3000/emit. To close the subscription server collection, call the GET http://localhost:3000/close API.