Shortest path algorithm, tests and Postman

- Added algorithm and endpoint to find the shortest path between two
  topics;
- Added respective test;
- Added a JSON collection with API calls that can be imported into
  Postman for the convenience of the user.

README.md

@@ -20,7 +20,11 @@ npm run start
 
 ## Usage
 
-You can use Postman or Curl to make calls to the API. The examples below use Curl.
+You can use Postman or Curl to make calls to the API.
+
+If using Postman, you can import the collection `ProjectMark.postman_collection.json` from the root.
+
+The examples below use Curl.
 
 ### Create a topic:
 
@@ -76,6 +80,24 @@ curl -X DELETE http://localhost:3000/api/topics/1234567890
 
 > Replace `1234567890` with the topic id.
 
+## Utilities
+
+### Retrieve topic and all its subtopics recursively
+
+```sh
+curl -X GET http://localhost:3000/api/topics/recursive/1234567890
+```
+
+> Replace `1234567890` with the topic id.
+
+### Shortest path between two topics in a tree
+
+```sh
+curl -X GET http://localhost:3000/api/topics/shortest/1234567890/0987654321
+```
+
+> Replace `1234567890` and `0987654321` with the topic ids.
+
 ## Tests
 
 Run tests with: