Allow linkcheck

[nedbat]

I love the tabs, but sphinx-tabs prevents linkcheck from succeeding:

WARNING: Not copying tabs assets! Not compatible with linkcheck builder

This simply adds linkcheck as a compatible builder so that they don't conflict.

[zxiiro]

We're experiencing this issue too as we have treat warnings as error in our Sphinx build. Would love to see this get included.

[Daltz333]

I think this can be closed, as you can add custom builders. An example of this is in the README

[chrisjsewell]

yeh I'm going to close this, since you can just use the sphinx_tabs_valid_builders config 😄