Add instructions for Windows and Linux

Author: mmicu

.gitignore

@@ -4,3 +4,5 @@ misc
 
 NOTES.md
 TODO.md
+
+artifacts/python-for-coding-interview-v*.pdf

USAGE.md

@@ -7,11 +7,10 @@ docker build -t pfci:latest .
 # Linter
 docker run --rm pfci:latest make linter
 # Generate PDF
-docker run --rm -v %cd%\artifacts:/repo/artifacts pfci:latest make pdf
+docker run --rm -v %cd%\artifacts:/repo/artifacts pfci:latest make pdf    # Windows
+docker run --rm -v $(pwd)\artifacts:/repo/artifacts pfci:latest make pdf  # Linux
 ```
 
-docker run --rm pfci:latest "make pdf &> /dev/null && ls /repos/" > ./artifacts/python-for-coding-interview.pdf
-
 ## Without docker
 
 ```text