lint: refactor final output message (#503)

Changes:
- Indent contents of triple-quoted string literals, using `unindent` or
  `dedent`. This improves readability, and consistency with other code.

- Move a block of code, to clarify that we currently only print the
  message about warnings when there were warnings but no errors.

src/lint/lint.nim

@@ -22,40 +22,40 @@ proc allChecksPass(trackDir: Path): bool =
   result = allTrue(checks)
 
 proc lint*(conf: Conf) =
-  echo "The lint command is under development.\n" &
-       "Please re-run this command regularly to see if your track passes " &
-       "the latest linting rules.\n"
+  echo """
+    The lint command is under development.
+    Please re-run this command regularly to see if your track passes the latest linting rules.
+  """.unindent()
 
   let trackDir = Path(conf.trackDir)
 
   const url = "https://github.com/exercism/docs/blob/main/building/configlet/lint.md"
 
   if allChecksPass(trackDir):
     echo """
-Basic linting finished successfully:
-- config.json exists and is valid JSON
-- config.json has these valid fields:
-    language, slug, active, blurb, version, status, online_editor, key_features, tags
-- Every concept has the required .md files
-- Every concept has a valid links.json file
-- Every concept has a valid .meta/config.json file
-- Every concept exercise has the required .md files
-- Every concept exercise has a valid .meta/config.json file
-- Every practice exercise has the required .md files
-- Every practice exercise has a valid .meta/config.json file
-- Required track docs are present
-- Required shared exercise docs are present"""
+      Basic linting finished successfully:
+      - config.json exists and is valid JSON
+      - config.json has these valid fields:
+          language, slug, active, blurb, version, status, online_editor, key_features, tags
+      - Every concept has the required .md files
+      - Every concept has a valid links.json file
+      - Every concept has a valid .meta/config.json file
+      - Every concept exercise has the required .md files
+      - Every concept exercise has a valid .meta/config.json file
+      - Every practice exercise has the required .md files
+      - Every practice exercise has a valid .meta/config.json file
+      - Required track docs are present
+      - Required shared exercise docs are present""".dedent()
+    if printedWarning:
+      echo ""
+      const msg = """
+        Configlet produced at least one warning.
+        These warnings might become errors in a future configlet release.
+        For more information, please see the documentation:""".unindent()
+      warn(msg, url, doubleFinalNewline = false)
   else:
-    echo &"""
-Configlet detected at least one problem.
-For more information on resolving the problems, please see the documentation:
-{url}"""
+    echo fmt"""
+      Configlet detected at least one problem.
+      For more information on resolving the problems, please see the documentation:
+      {url}""".unindent()
     quit(1)
-
-  if printedWarning:
-    echo ""
-    const msg = """
-      Configlet produced at least one warning.
-      These warnings might become errors in a future configlet release.
-      For more information, please see the documentation:""".unindent()
-    warn(msg, url, doubleFinalNewline = false)