Lint docs as part of CI

[conorsch]

Feature Request

Description

The docs are automatically built from merged PRs and hosted on ReadTheDocs. We aren't testing the docs in any way via CI right now. We should:

• build the docs to confirm no failures
• lint the docs for common ReST errors

A patch such as the following would suffice:

.PHONY: docs-lint
docs-lint: ## Check documentation for common syntax errors.
# The `-W` option converts warnings to errors.
# The `-n` option enables "nit-picky" mode.
make -C docs/ clean && sphinx-build -Wn docs/ docs/_build/html

That example is lifted from similar work over in the SecureDrop repository. A new Makefile target such as the above should be appended to the CI config at circle.yml.

User Stories

As as a developer, I want CI to catch common formatting mistakes prior to merging.

As a maintainer, I want to encourage well-structured documentation for the project, particularly for newcomers.