Fix syntax highlighting

README.md

@@ -14,7 +14,7 @@ Installing
 
 Preferably, you would use a separate virtual env
 
-```
+```bash
 pip install -r requirements.txt
 pip install -e .  # installs the 'psh' package in editable mode
 ```
@@ -30,7 +30,7 @@ main()
 ```
 
 From Unix shell:
-```
+```bash
 python -m psh.run
 ```
 
@@ -39,6 +39,6 @@ Testing
 
 From Unix shell:
 
-```
+```bash
 py.test
 ```