F/added linux start command

[Blackstareye]

I saw in #7 that there is no start setup for linux users.

So I added a simple script which installs the routines discussed in #7. It only installs the venv again if there is no venv installed.

I also added an error if no python3.8 is found.

Another issue was, that only chrome was allowed in eel. Hence many linux users neither use chrome nor edge, firefox is a better choice. So I added the browser as an sysargv argument.

Hope this PR makes the usage in other os more convenient