Clarify documentation of "attribute_name"

[exhuma]

It was not immediately clear to me that attribute_name is subsequently used to bind with that attribute.

The process (from going through a debugger) is as follows:

• Use the bind-user to execute a search
• Extract the attribute_name from the matching results
• Attempt to bind using whatever results from that as DN, and using the password supplied by the user

The attribute I specified in the config did not return the DN of the user, but rather a "human-readable" name making the second bind-attempt failing. By simply specifying that attribute_name should contain the name of the attribute which contains the user's DN would have helped a lot.

[fschulze]

Could you make a PR? A PR done through the web interface of GitHub works just fine. Thanks in advance!

[exhuma]

Done: See #46

[fschulze]

Thanks! I will close this issue after next release.