Merge pull request cosmicpython#30 from GeyseR/patch-1

fix requirements installation command in README

Author: hjwp

Diff for: README.md

@@ -45,10 +45,10 @@ pip install pytest
 pip install pytest sqlalchemy
 
 # for chapter 4+5
-pip install requirements.txt
+pip install -r requirements.txt
 
 # for chapter 6+
-pip install requirements.txt
+pip install -r requirements.txt
 pip install -e src/
 ```