Add example for markdownlint-rule-helpers.applyFixes to documentation (fixes #663).

README.md

@@ -928,6 +928,14 @@ bad.md: 1: MD041/first-line-heading/first-line-h1 First line in a file should be
 
 <!-- markdownlint-restore -->
 
+### Fixing
+
+Rules that can be fixed automatically include a `fixInfo` property which is
+outlined in the [documentation for custom rules](doc/CustomRules.md#authoring).
+To apply those fixes more easily, the `applyFixes` method in
+[markdownlint-rule-helpers](helpers/README.md#applying-recommended-fixes) may
+be used.
+
 ## Browser
 
 `markdownlint` also works in the browser.

helpers/README.md

@@ -17,7 +17,9 @@ change from release to release. There are brief descriptive comments above each
 function, but no [JSDoc][jsdoc] annotations. That said, some of what's here will
 be useful to custom rule authors and may avoid duplicating code.
 
-## Example
+## Examples
+
+### Using Helpers from a Custom Rule
 
 ```javascript
 const { forEachLine, getLineMetadata } = require("markdownlint-rule-helpers");
@@ -41,6 +43,18 @@ module.exports = {
 };
 ```
 
+### Applying Recommended Fixes
+
+```javascript
+const { "sync": markdownlintSync } = require("markdownlint");
+const markdownlintRuleHelpers = require("markdownlint-rule-helpers");
+
+function fixMarkdownlintViolations(content) {
+  const fixResults = markdownlintSync({ strings: { content } });
+  return markdownlintRuleHelpers.applyFixes(content, fixResults.content);
+}
+```
+
 See also: [`markdownlint` built-in rule implementations][lib].
 
 ## Tests

test/markdownlint-test.js

@@ -679,6 +679,7 @@ test("readmeHeadings", (t) => new Promise((resolve) => {
           "#### callback",
           "#### result",
           "## Usage",
+          "### Fixing",
           "## Browser",
           "## Examples",
           "## Contributing",