Bug Fix, Code Improvements, README.md Updates

Bug Fix
---
In ```tftpd.py``` the default IP was set to ```ip=''``` which doesn't really specify which IP it should bind to. By changing the default IP to ```ip='0.0.0.0'``` then the TFTP server binds to all available IPs the machine has and can be made available on the network to all of those IPs (provided no firewall is blocking, of course).

Code Improvements
---
**Thread Improvements**
In ```server.py``` the ```while True:``` was changed to refelect the status of the individual threads rather than just an arbitray True value.
**README.md Updates**
Some README.md updates for better explanation and formatting so that users can better understand what is going on and where files/directories comes from