Add example of passing header to Cache Invalidator

[calumbrodie]

No description provided.

[dbu]

can you break this on multiple lines please?

and can you add a similar note to the one ddboer did on the proxy doc, that you should not use this for headers that are always the same.

[calumbrodie]

@stof Thanks (I did wonder what the failed build was about). Is there a quicker way to validate the documentation other than attempting to build it with sphinx (for next time)?

[stof]

@calumbrodie not that I know of (which is why our Travis build is building it)

[stof]

Please don't remove the empty line between the reference and the title

[dbu]

@stof https://github.com/stof Thanks (I did wonder what the failed
build was about). Is there a quicker way to validate the documentation
other than attempting to build it with sphinx (for next time)?

if you just do the occasional fix, travis is fine. when starting to
write whole doc sections, i just installed sphinx - its not that hard,
and once you have it running, its very easy to build locally. i
installed it according to http://sphinx-doc.org/ and then its just make html.