Update readme, add auto-install and exec bit.

These are just some changes I think will be helpful. I think the one-liner install is especially simple for beginners.

- Update the readme to be more clear and readable.
- Add execution bit so that script can be called as ```./script```. Right now it only works as ```python script.py```.
- Add a single one-liner so people can just quickly install it.

Note that the ```curl ... | sudo sh``` command will work once it's been merged
in, since I've already pointed it at your repo.

If you want to test it you can run:
```bash
curl "https://raw.github.com/stephendotexe/stratum-mining-proxy/master/auto_install.sh" | sudo sh
```