Update URL-Shortener-Microservice Hint Markdown (#36299)

Creating a Hinting for this project with useful tips

guide/english/certifications/apis-and-microservices/apis-and-microservices-projects/url-shortener-microservice/index.md

@@ -3,8 +3,24 @@ title: URL Shortener Microservice
 ---
 ## URL Shortener Microservice
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/apis-and-microservices/apis-and-microservices-projects/url-shortener-microservice/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
+The core features to complete this exercise are the creation and retrieval of URLs from the Database.
 
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
+## Creating Short URL
+- Connect to your database instance.
+    > **Note**: It's important to check your Mongoose connection status before dive into the problem, just to check if everything is okay with your database configuration. This should help: `mongoose.connection.readyState`
+- Receive a POST request containing an URL to be saved on Database.
+- Check if it is a valid URL using `dns.lookup(url, callback)`
+    - Remember you need to import the dns module with required.
+- Generate some kind of identifier to save your original URL in database.
+    - A SHA-1 hash could be used, or even the object ID when saving the element.
+    - There is a bunch of samples over the internet how to generate some kind of identifier, try to explore it or create your own.
+    - An example of how this should look like: `{'url': www.freecodecamp.org, 'hash': 'ef49fa8b4'}`
+    
+## Retrieving Short URL
+- Receive a GET request containing an identifier used to find a stored URL.
+- Try to find one URL saved for this identifier
+- Redirect user to URL.
+    > **Note**: The `res.redirect(url)` function need that the given url, has a defined protocol (http://, https://), or it will just concatenate it as an extension of your current domain. eg: Good URL: `https://www.freecodecamp.org`, Bad URL: `www.freecodecamp.org`. Try it out.
+- Remember to handle error situations with proper response like, `res.json({"error":"invalid URL"});
 
 <!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->