Added C11 option to template

[siddharthzs654]

This is a follow up update, where C11 lang option was added to the list in views.py

[sahildua2305]

Hi @siddharthzs654, thanks for this contribution! There are a couple of things missing for this to be complete:

1. You'll need to add C11 as one of the permitted languages here otherwise it will be rejected by the hackIDE server.
2. I'd suggest adding a boilerplate code same as the one for CPP here.

And finally, please share a screenshot verifying that the newly added CPP11 language actually works.