Wrong conda panda-dev env filepath in "Creating a Python Environment" docs
One of the first steps in the Contributing to Pandas guide is [Creating a Python Environment](http://pandas.pydata.org/pandas-docs/stable/contributing.html#creating-a-python-environment). The first line regers to a yaml file inside `ci/` but that files seems to have been [moved to the project root](https://github.com/pandas-dev/pandas/blob/master/environment.yml).
```
# Create and activate the build environment
conda env create -f ci/environment-dev.yaml
...
```
Should be
```
# Create and activate the build environment
conda env create -f environment.yml
...
```