linkchecker: add page (#3611)

pages/common/linkchecker.md

@@ -0,0 +1,20 @@
+# linkchecker
+
+> Command line client to check HTML documents and websites for broken links.
+> More information: <https://linkchecker.github.io/linkchecker/>.
+
+- Find broken links on https://example.com/:
+
+`linkchecker {{https://example.com/}}`
+
+- Also check URLs that point to external domains:
+
+`linkchecker --check-extern {{https://example.com/}}`
+
+- Ignore URLs that match a specific regex:
+
+`linkchecker --ignore-url {{regex}} {{https://example.com/}}`
+
+- Output results to a CSV file:
+
+`linkchecker --file-output {{csv}}/{{path/to/file}} {{https://example.com/}}`