Add param documentation for overwrite_if_exists

[inktrap]

Seems you missed it so it won't show up here:
https://cookiecutter.readthedocs.io/en/stable/cookiecutter.html#cookiecutter.main.cookiecutter

[inktrap]

But skip_if_file_exists is also not documented and if I look at the API docs it seems to be undocumented by choice. Other paramters with default values however are documented. What's you preferred way of doing this?

[inktrap]

I just wanted to clarify: while the params are documented through the options: https://cookiecutter.readthedocs.io/en/stable/cli_options.html I looked for a way to combine two different cookiecutter templates and then to use the result. That way I can write my own additions without the need to fork a project. This should work pretty well with a minimal base cookiecutter.

For that to work I would have to know if overwriting is some kind of merging (files are overwritten as they are encountered) or if it is a fresh start (the whole directory is removed and then recreated).

Obviously I can figure this out by reading the source, just wanted to explain why it would be good if kind of obvious parameters had some docs too

[kurtmckee]

@jensens @pydanny @ssbarnea Please merge this PR.

It addresses missing parameter documentation so the parameter will appear in the API docs.