adding supervisor process control installation instruction (#668)

* adding supervisor process control installation instruction

* adding supervisord official website

* adding secret file generation document

* adding secret file generation document

* typo correction

* typo correction

* typo correction

* typo correction

docs/src/tutorials/93--Deploying_Genie_Using_A_Process_Control_System.md

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+# Deploying Genie apps using:  A Process Control System
+
+This tutorial shows how to host a Julia/Genie app using process control system. We using `supervisor`  for this tutorial.
+
+## Prerequisites
+
+Install `supervisor` in system. If you not sure how to install you can find the suitable command from [here](https://command-not-found.com/supervisord)  or you can [refer to official website](http://supervisord.org/)
+
+## The application
+
+We assume that a Genie app has been developed and is ready for deployment and that it is hosted as a project on a git repository.
+
+For example, the app `MyGenieApp` generated through `Genie.Generator.newapp("MyGenieApp")` being hosted at
+`github.com/user/MyGenieApp`.
+
+The scripts presented in this tutorial are for Ubuntu 20.04.
+
+## Install and run the Genie app on the server
+
+Access the server:
+
+```shell
+ssh -i "ssh-key-for-instance.pem" [email protected]
+```
+
+Install Julia if not present. Then make the clone:
+
+```shell
+git clone github.com/user/MyGenieApp
+cd MyGenieAp
+```
+
+Install the app as any other Julia project:
+
+```shell
+julia
+] activate .
+pkg> instantiate
+exit()
+```
+
+In order to launch the app using `supervisor` you have to create `genie-supervisor.conf` file or you can name it something else with file name ending `.conf` as extension at project directory path.
+
+
+```shell
+[program:genie-application]
+process_name=%(program_name)s_%(process_num)02d
+command= ./bin/server
+autostart=true
+autorestart=true
+stopasgroup=true
+killasgroup=true
+numprocs=1
+redirect_stderr=true
+stdout_logfile=/var/log/genie-application.log
+stopwaitsecs=3600
+```
+
+Now the application is almost ready to start just need to configure [the secret token](https://genieframework.github.io/Genie.jl/dev/API/secrets.html#Genie.Secrets.secret_token). Go into the project directory and execute the following command. It will generate `secrets.jl` inside `config/secrets.jl` file and if it exists then it will update with a new token string.
+
+```sh
+julia --project=. --banner=no --eval="using Pkg; using Genie; Genie.Generator.write_secrets_file()"
+```
+
+
+Then set the `GENIE_ENV` environment variable to `prod`:
+
+```shell
+export GENIE_ENV=prod
+```
+
+To launch the app few things need to do before starting process control.
+
+Create symbolic link to supervisor config directory
+```shell
+cd /etc/supervisor/conf.d/
+sudo ln -s /PATH TO THE SUPERVISOR.CONF FILE
+sudo /etc/init.d/supervisor reload
+```
+
+
+### Few assumption about installation instruction
+- In this tutorial above configuration is done at `Debian` or `Ubutu` server and tested well
+- `GENIE_ENV=prod` should be exported before you run the application else it will take default `GENIE_ENV` environment
+
+
+### If thing not working then you may check following things.
+
+(1) check the `sudo systemctl status supervisor.service` service is working or not. if not working then you can start and enable for the start up using following command
+
+```shell
+sudo systemctl enable supervisor.service
+sudo systemctl start supervisor.service
+```
+
+and then check if status is active or still has any issue.
+
+(2) You can check the application log by tail to log file as bellow
+
+```shell
+tail -f /var/log/genie-application.log
+```
+
+in this log you will find the genie logs.
+
+(3) Make sure whatever port you used inside `GENIE_ENV` config file at `server_port` must be open in  at firewall and no other process is bind to it.
+
+Check weather the any process is running at port 80 for an example use following command
+
+```shell
+sudo lsof -t -i:80
+```
+
+If you want to kill the process which is running at port 80 you can use single liner magic command
+
+```shell
+if sudo lsof -t -i:80; then sudo kill -9 $(sudo lsof -t -i:80); fi
+```