Monthly report: add QA check in the publishing process.

We've recently published reports with broken links and reports
that simply broke the build of the website. Let's try harder to notice that
before publishing.

wiki/src/blueprint/monthly_report.mdwn

@@ -66,7 +66,11 @@ Publishing
   - Ensure the `meta date=` directive is set to today's date in RFC 2822 format
     (e.g. `date --rfc-2822`).
   - Move report to `news/report_YEAR_MO.mdwn`.
-  - Commit and push.
+  - Commit.
+  - Build the website locally and check that it builds fine and the
+    report renders well (e.g. no broken links that worked only earlier
+    because the report was under `blueprints/`).
+  - Push.
   - Tweet about the report:
        - "In MONTH we worked on [...] and more: https://tails.boum.org/news/report_YEAR_MO."
        - If you don't have access to our Twitter account send your text