Add instructions in README to run locally with Python 3

Author: ablazejuk

README.md

@@ -2,12 +2,20 @@
 
 ## Production environment
 
-https://ablazejuk.github.io/musicians-helper/
+[https://ablazejuk.github.io/musicians-helper/](https://ablazejuk.github.io/musicians-helper/)
 
 ## Run Locally
 
-```
+### Python 2
+
+```python
     python -m SimpleHTTPServer 8000
 ```
 
-Open http://localhost:8000/ in your browser.
+### Python 3
+
+```python
+    python -m http.server 8000
+```
+
+Open [http://localhost:8000/](http://localhost:8000/) in your browser.