Added input download instructions to README

README.md

@@ -6,15 +6,21 @@ To solve all puzzles with implemented solutions run
 ```console
 $ python3 main.py 
 ```
-or alternatively make the main program executable.
+For faster execution use `pypy3`
+```console
+$ pypy3 main.py
+```
+or make the main program executable.
 ```console
 $ chmod +x main.py
 $ ./main.py
 ```
-For faster execution use `pypy3`.
-```console
-$ pypy3 main.py
-```
+To download your puzzle inputs (the inputs are different for each user),
+run `./main.py --fetch-session` and input your session key.
+The session key can be found by inspecting the headers of a HTTP request
+made from a browser on which the user is logged in. The HTTP request header
+in question has the following format : `Cookie : session=key`.
+
 For other options see `./main.py -h`.
 ```console
 $ ./main.py -h