add "How to buid" section to your readme

Sth like

### Debian based Linux
```
sudo apt install default-jdk maven git
#cd somewhere where you like to the source to be build
git clone https://github.com/DavyCraft648/Barrel
cd Barrel
mvn install
```

or so
### Windows
what you have to do there

also prebuild releases would be nice

thanks in advance