Add section for DataCollection to ooni website

From the parent ticket comment:

"This needs to be more thoroughly documented and linked to the oonib documentation. For example, there should be a page describing the report format, and also link to the backend setup and use of ooni-probe with a collector."

and

"It should have its own page with sections for setting up the backend (similar to or taken from oonib/README.md) and test helpers, and document what each test helper does."

Create a new section "Data Collection" on ooni.torproject.org with the following subsections:

Report Format Deploying OONIB and Test helpers Archiving reports

This latter two items might be as resolved by simply sourcing the oonib/README.md file