Enforce EIPs must have an appropriate filename.

[MicahZoltu]

Filename should be EIPS/eip-####.md where #### matches the header eip file.

[mryalamanchi]

@MicahZoltu, is it necessary that # in the eip-# has to be a 4-digit number?
@lightclient I would like to pick up this task and submit a PR. This will help me with documenting the EIP bots' workflow.

[lightclient]

Feel free to take a stab and open a PR. The number does not have to be 4 digits (e.g. eip-20.md).

[mryalamanchi]

Thanks.