This seems to be a copy & paste artifact, as the configuration keys
itself are spelled correctly, but the comment describing this block is
wrongly suggesting that the following block is about `file-crlf` (rather
than `file-nullbyte`).

README: Fix a typo in the example configuration file

…iles

This updates the recommended / suggested configuration file presented in
the `README.md` file, so that `file-nullbyte` is only searching text
files by default (`FILE_NULLBYTE_TEXT=0).

Searching binary files for null bytes (`NUL`) makes not too much sense,
since it will regularly find such files, and it is perfectly fine for
them to contain these bytes.

This addresses one aspect of an issue with searching binary files with
this particular file check (documented in #14).

Currently the repo label is set to a different repository, which was probably
a copy & paste mistake in the beginning. The URL for this repository is
`https://github.com/cytopia/docker-file-lint`, so this commit changes it.

README: Change recommendation for file-nullbyte to only search text files

Dockerfile: Set correct URL for repo label

Release 0.4