Add requirements.txt file watching.

grunt-config/shell.js

@@ -4,5 +4,8 @@ module.exports = {
     },
     bower_install: {
         command: 'bower install'
+    },
+    pip_install: {
+        command: 'pip install --upgrade --requirement requirements.txt'
     }
 };

grunt-config/watch.js

@@ -9,5 +9,9 @@ module.exports = {
     },
     gruntfile: {
         files: ['Gruntfile.js']
+    },
+    requirements: {
+        files: ['requirements.txt'],
+        tasks: ['shell:pip_install']
     }
 };