[ADF-2447] Added review checker tool (#3039)

lib/config/DocProcessor/ReviewCheckerGuide.md

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+# Review checker guide
+
+The review checker tool queries the Github repo to look for recent
+commits to the component source files. The dates of these commits
+are compared against against a review date stored in the Markdown doc
+file for each component. The time and the number of commits since the
+last review are then combined into a "score" that gives an indication
+of how urgently the doc file needs a review.
+
+## Review date metadata
+
+The review date is kept in the YAML metadata section at the top of each
+Markdown file. The key is "Last reviewed" and the date is in the form
+YYYY-MM-DD.
+
+## Commit message stoplist
+
+The checker will ignore any commits that match regular expressions stored
+in the `commitStoplist.json` file in the `DocProcessor` folder. You could
+use this, for example, to filter out JIRA tasks that don't involve any
+changes in functionality (and therefore don't need documenting).
+
+## Output format
+
+The script sends comma-separated text to the command line. You can copy/paste
+this into a spreadsheet or redirect the output to a text file with a ".csv"
+suffix.