Added warning for NaNs

[Bhairvi23]

Added warning for the first encountered NaN value.
Closes #200

[observingClouds]

Hi @Bhairvi23,
Thank you for your first contribution to xbitinfo 🎉 The PR looks good so far and the failure seems to come from the newest changes to xarray. Before this contribution can be merged we need to do a few more things:

• remove the .DS_Store file that has been accidentally been committed
• add your changes to the CHANGELOG.md
• add a simple test to check whether or not the warning will actually be raised.

[observingClouds]

@Bhairvi23 I just updated your branch with a fix for the doctests. Now the tests all pass 🎉 If you could address above mentioned points we are ready to merge this.

[Bhairvi23]

@observingClouds I am unable to find the .DS_Store file. I can see that there has been some changes but I cant seem to locate it.

[observingClouds]

Hi @Bhairvi23 ,
The file is likely hidden on your system. You can see it with ls -a. To remove the file from your PC and the git you could do git rm .DS_store and commit the changes afterwards as usual.

[milankl]

.DS_Store is a hidden file that macos creates to store information of how to visualise a folder (e.g. list vs icons). It can generally be put into .gitignore

[milankl]

The .DS_Store file is still in the commits though, @Bhairvi23 can you try to delete it? It doesn't show up for me for some reason...

[observingClouds]

Sry @Bhairvi23 I just recognise that this issue will already be addressed with #260 which was unfortunately not linked to #200