Make documentation searchable

Whereas:

• Our documentation is difficult to search through. I'm specifically referring to materials on doc.gitlab.com, but the same will apply to materials being gathered on about.gitlab.com/university.
• Having great documentation that is easily searchable is a key component of shifting the burden of support tasks from individual responses to self-serve searches.

Therefore:

• We should make our documentation easier to search through.

I've heard that swiftype, and/or algolia are possible tools to use. We need someone to determine which tool will work, and what the steps to implementation are.

\cc @dblessing @patricio @balameb @kelvinmutuma @JobV @sytses