Added Hetzner Cloud keywords

[paulvollmer]

At first, thanks for this great terraform language package!

I added keywords for the hetzner cloud provider to the keywords.cson file.
my snippets are a bit different because i added the link to the website docs and the first sentence of the do to each keyword.

this was done by hand but i think it's not a big thing to write a small script to fetch the docs for each provider and grab the data we need from the html and markdown files.

for example all links for the hcloud keywords you can find here:
https://github.com/terraform-providers/terraform-provider-hcloud/blob/master/website/hcloud.erb

then it should be also possible to generate the keywords for all the providers and keep it easily up to date.

at the moment for me it looks like a lot of work to maintain...