Add a test to check for dashes in docs directory names

scripts/lint-doc.sh

@@ -81,6 +81,22 @@ then
   ((ERRORCODE++))
 fi
 
+# Do not use dashes (-) in directory names, use underscores (_) instead.
+# Number of directories with dashes as of 2021-09-17
+NUMBER_DASHES=2
+FIND_DASHES=$(find doc -type d -name "*-*" | wc -l)
+echo '=> Checking for directory names containing dashes...'
+echo
+if [ ${FIND_DASHES} -ne $NUMBER_DASHES ]
+then
+  echo
+  echo '  ✖ ERROR: The number of directory names containing dashes has changed. Use underscores instead of dashes for the directory names.' >&2
+  echo '  ✖        If removing a directory containing dashes, update NUMBER_DASHES in lint-doc.sh.' >&2
+  echo '  https://docs.gitlab.com/ee/development/documentation/styleguide/index.html#work-with-directories-and-files'
+  echo
+  ((ERRORCODE++))
+fi
+
 # Run Vale and Markdownlint only on changed files. Only works on merged results
 # pipelines, so first checks if a merged results CI variable is present. If not present,
 # runs test on all files.