Adding a note to install landlab_dev wiki

[pfeiffea]

I recently did a re-install of anaconda and the landlab development code as per the instructions on:
https://github.com/landlab/landlab/wiki/Installing-Landlab-from-source-code-(%22developer-install%22)

It took a hint from @kbarnhart, though, to realize that I needed to run conda install spyder (and then spyder) while in the landlab_dev environment in order run an instance of spyder that can access landlab. It might be nice to include a more generalized note about this on the landlab source code wiki page.