[Doc] Add work flow of checking broken links (apache#5529)

site2/README.md

@@ -35,6 +35,25 @@ cd pulsar/site2/website
 yarn test
 ```
 
+### Check
+
+Before submitting a pull request, run the following command to make sure no broken links exist.
+
+```
+cd pulsar/site2/website
+yarn build
+```
+
+If warning messages are shown as below, it means broken links exist.
+
+```
+[WARN] unresolved links in file 'version-2.4.1/getting-started-standalone.md' > [ 'security-overview.md' ]
+
+[WARN] unresolved links in file 'version-2.4.0/io-managing.md' > [ 'functions-overview.md' ]
+```
+
+Fix the broken links manually and then send a pull request.
+
 ## Documentation
 Pulsar documents are written in English. Documentation related pages are placed in the `/site2/docs` directory. All documentation pages are versioned. For more details, refer to [versioning](#versioning).
 
@@ -256,4 +275,4 @@ The translated docs are downloaded to the `site2/website/translated_docs` direct
 ### Check issues, fix and verify
 
 After download the translated documents, you can open the target markdown file, check issues and fix them.
-To verify if you have fixed the issues correctly, [run the site locally](#run-the-site-locally).
+To verify if you have fixed the issues correctly, [run the site locally](#run-the-site-locally).