Add documentation on how to create fixtures

[david-a-wheeler]

It would be great to have some specific documentation on how to create fixtures, particularly to warn about the trailing new lines.

I intend to submit a pull request to do this, but if there are any particular issues or things that should cover, please reply here. If you think that is out of scope for the documentation, let me know that too.

I intend to use this issue as a starting point:

#2

[ankane]

Added a section on fixtures here (along with a cleaner way to generate the bidx): https://github.com/ankane/blind_index#fixtures

[david-a-wheeler]

I like the additional section, but I think it is really important to mention the need fir a trailing newline there. That is a not immediately obvious to a new user of the gem. I would have something like this...

The inspect method is required because blind indexes always end in a new line, and without the inspect method the newline would not be provided by the yaml file.

[ankane]

Good call, I added more emphasis on the inspect part.

[david-a-wheeler]

The addition is good, but I still think it needs to specifically mention the trailing newlines. Otherwise it won't be obvious WHY the encoding is important. Thanks