add basic readme to repo

README.md

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+# RHMI SMTP Tooling and Service
+
+This repo is intended to store the services and tooling related to the setup of
+SMTP in an Integreatly/RHMI cluster.
+
+## CLI
+
+This repo contains a CLI which can be used to create SendGrid sub users and API
+keys for those sub users, that can be used with RHMI clusters.
+
+The intended pattern is that each RHMI cluster would have it's own sub user
+which would then contain an API key for the RHMI cluster. The reasoning behind
+this approach is that *SendGrid clusters only allow 100 API keys per user*.
+
+### Building
+
+To build the CLI, run from the root of this repo:
+
+```
+make build/cli
+```
+
+A binary will be created in the root directory of the repo, which can be run:
+
+```
+./cli
+```
+
+
+### How to use
+
+To use the CLI, you must create the env var `SENDGRID_API_KEY`, with a SendGrid master account API key with at least
+permissions to:
+
+- Create and read sub users
+- Create and read API keys
+- Read IP addresses
+
+To export the env var, run:
+
+```
+export SENDGRID_API_KEY=<mySendGridAPIKey>
+```
+
+#### Create a new API key for a cluster
+
+To create a new API key for a cluster, run:
+
+```
+./cli create my_cluster_id
+```
+
+an OpenShift Secret will be output to stdout.
+
+Note that the cluster name must also be a unique username is SendGrid.
+
+#### Delete an API key for a cluster
+
+To delete an API key for a cluster, run:
+
+```
+./cli delete my_cluster_id
+```
+
+This will simply delete the sub user associated with the SendGrid cluster.
+
+#### Get an API key for a cluster
+
+To get the name of the API key for a cluster, not the cluster itself, run:
+
+```
+./cli get my_cluster_id
+```
+
+This command is mainly useful to check if an API key exists for the cluster.
+
+## Testing
+
+To run unit tests, run:
+
+```
+make test/unit
+```