update contributing and readme to reflect the move away from slack to…

… gitter

CONTRIBUTING.md

@@ -6,5 +6,5 @@ If you are interested in contributing to pylj. Please feel free; fork the code a
 
 - We are trying to use a modular system within pylj, where there is the overarching `util` module that contains the `System` class which holds all system information. Examples of modules that use the `System` class are the `md` and `mc` module that facilite molecular dynamics and Monte-Carlo simulation respectively. 
 - All visuallisation should be done in the `sample` module, the structuring of this module should be clear and generally the only variable required should be the `System` class object. 
-- If you want any help implementing your idea, please feel free to discuss it on our [Slack channel](https://pylj.slack.com). We prefer this method of communication over email, however if you are morally or structurally aposed to Slack feel free to email [arm61](mailto:arm61@bath.ac.uk).
+- If you want any help implementing your idea, please feel free to discuss it on our [gitter channel](https://gitter.im/pylj/Lobby#). We prefer this method of communication over email, however if you are morally or structurally aposed to gitter feel free to email [arm61](mailto:arm61@bath.ac.uk).
 - If you would like to offer a pull request, we will try our best to assess and merge them as appropriate in a timely manner. 

README.md

@@ -16,7 +16,7 @@ python setup.py test
 
 ```
 
-All development discussion can take place on [gitter](https://gitter.im/pylj/Lobby#).
+If you need any help using pylj contact arm61 in the [pylj/HELP gitter chatroom](https://gitter.im/pylj/HELP).
 
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