docs: add README

README.md

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+# cy-smtp
+
+This is a small binary to test the connection to a SMTP server.
+If all works well, running `cy-smtp` will send to the specified recipient this test email:
+
+```
+Hello from cy-smtp!
+This is a test message.
+```
+
+You can pass all the needed parameters on the command line, in this case check the help of the command, `cy-smtp --help`.
+Or the `config.yaml` file to configure the behavior, the parameters in the YAML file are mostly compatible with the ones used by Cycloid.
+There are two addition: `email-tls-skip-verify` and `email-addr-to`. If you are using the Cycloid config file these two parameters must be passed on the cmd line or added int the config file.
+
+