Changes the install instructions for Mac OSX. Thank you to Sophie Gresham for making me aware of this

Author: StuntsPT

docs/install.md

@@ -15,7 +15,7 @@ Due to the way different Operating Systems handle dependencies specific instruct
 1. Install python 3. MacOS comes with python 2.7 installed by default, (Mac OSX versions before "Sierra" does not have any version of python installed) but in order to run *Structure_threader* you will need python 3.4 or above. You can [follow this comprehensive guide to do it](http://python-guide-pt-br.readthedocs.io/en/latest/starting/install3/osx/).
 2. Install `pip`. `pip` is a [package manager for python](https://en.wikipedia.org/wiki/Pip_(package_manager)). You can use the guide from step 1 to install it on your system.
 3. Install *Structure_threader*. Now that you have python 3 and `pip` installed, installing *Structure_threader* is just one terminal command away: `pip3 install structure_threader --user`. The `--user` option installs the software to a local directory, ensuring you do not need administration privileges to perform the installation.
-4. Using *Structure_threader*. Running the command from step 3 will install the program to `~/.local/bin`. You can either run it by calling it directly `~/.local/bin/structure_threader` or by adding the location `~/.local/bin` to your shell `$PATH` ([here is a good guide on how to do it](https://unix.stackexchange.com/questions/26047/how-to-correctly-add-a-path-to-path))and just calling `structure_threader`. Also note that on MacOS installing *Structure_threader* will also automatically install binaries for *STRUCTURE*, *fastStructure* and *MavericK*, which will also be placed under `~/.local/bin`.
+4. Using *Structure_threader*. Running the command from step 3 will install the program to `~/.local/bin` (or, under some versions, under `~/Library/Python/3.6/bin`, where `3.6` will change according to the version of `python` you are running). You can either run it by directly calling `~/.local/bin/structure_threader` (or `~/Library/Python/3.6/bin/structure_threader`) or by adding the location `~/.local/bin` (or `~/Library/Python/3.6/bin`) to your shell `$PATH` ([here is a good guide on how to do it](https://unix.stackexchange.com/questions/26047/how-to-correctly-add-a-path-to-path))and just calling `structure_threader`. Also note that on MacOS installing *Structure_threader* will also automatically install binaries for *STRUCTURE*, *fastStructure* and *MavericK*, which will also be placed under `~/.local/bin` (or `~/Library/Python/3.6/bin/structure_threader`).
 
 ### Windows