[Documentation] Add example deploy session (#2)

Reviewed-on: #2

deploy_configs/README.md

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+# Deployment command line example
+
+Example terminal session for deploying. ssh to your VPS and follow along. Minor differences may be required. e.g. if you are already root, skip `sudo`. If curl is missing, use wget.
+
+## Check python version
+
+Python version should be a supported (as of now 3.9 and above)
+```sh
+python3 -V
+```
+
+## Choose release
+```sh
+RELEASE=v1.0
+```
+
+## Download App
+```sh
+curl -OL "https://gitea.balki.me/balki/mail4one/releases/download/$RELEASE/mail4one.pyz"
+chmod 555 mail4one.pyz
+```
+
+## Download sample configurations
+```sh
+curl -OL "https://gitea.balki.me/balki/mail4one/raw/tag/$RELEASE/deploy_configs/mail4one.service"
+curl -OL "https://gitea.balki.me/balki/mail4one/raw/tag/$RELEASE/deploy_configs/mail4one.conf"
+curl -OL "https://gitea.balki.me/balki/mail4one/raw/tag/$RELEASE/deploy_configs/mail4one_cert_copy.sh"
+```
+
+## Generate Password hash
+
+This can be done in any machine. Do this once for each user. Every time a new hash is generated as a random salt is used. Even if you are using the same password for multiple clients, it is recommended to generate different hashes for each.
+
+```sh
+./mail4one.pyz -g
+./mail4one.pyz -g <password> # also works but the password is saved in the shell commandline history
+```
+
+## Generate config.json
+
+Edit [config.sample](config.sample) in your local machine and convert to config.json (See [here](./config.sample#L5) for some tools).
+
+Then copy the config.json to your vps
+```sh
+scp config.json user@vps:~/
+# or run below in vps terminal
+cat > config.json
+<paste json config from clibboard
+<Ctrl + D>
+
+# move to /etc
+
+# This should show number of lines in your config
+wc -l config.json
+sudo mv config.json /etc/mail4one/config.json
+```
+
+## Create mail4one user
+
+```sh
+sudo mkdir -p /etc/sysusers.d/
+sudo cp mail4one.conf /etc/sysusers.d/
+sudo systemctl restart systemd-sysusers
+# This should show the new user created
+id mail4one
+```
+## Copy app
+```sh
+sudo cp mail4one.pyz /usr/local/bin/mail4one
+# This should show executable permissions and should be owned by root
+ls -l /usr/local/bin/mail4one
+```
+
+## Setup mail4one.service
+```sh
+sudo cp mail4one.service /etc/systemd/system/mail4one.service
+sudo systemctl daemon-reload
+sudo systemctl enable --now mail4one.service 
+systemctl status mail4one
+```
+Above command should fail as the TLS certificates don't exist yet.
+
+## Setup TLS certificates 
+Install [certbot](https://certbot.eff.org/) and run below command. Follow instructions to create TLS certificates. Usually you want certificate for domain name like `mail.example.com`
+```sh
+sudo certbot certonly
+sudo cp /etc/letsencrypt/live/mail.example.com/{fullchain,privkey}.pem  /var/lib/mail4one/certs/
+sudo chown mail4one:mail4one /var/lib/mail4one/certs/{fullchain,privkey}.pem
+
+# Edit mail4one_cert_copy.sh to update your domain name
+sudo cp mail4one_cert_copy.sh /etc/letsencrypt/renewal-hooks/deploy/
+sudo chmod +x /etc/letsencrypt/renewal-hooks/deploy/mail4one_cert_copy.sh
+```
+## Restart service and check logs
+```sh
+sudo systemctl restart mail4one.service
+systemctl status mail4one.service
+cat /var/log/mail4one/mail4one.log
+```
+
+## Testing dns and firewall
+In vps
+```sh
+mkdir test_dir
+touch test_dir/{a,b,c}
+cd test_dir
+python3 -m http.server 25
+```
+In local machine or a browser
+You should see file listing a, b, c. Repeat for port 465, 995 to make sure firewall rules and dns is working 
+```sh
+curl http://mail.example.com:25
+```
+If not working, refer to VPS settings and OS firewall settings.