added example of context manager use

context_managers.py

@@ -0,0 +1,17 @@
+from fabric.api import env, run, cd, settings, local
+
+env.roledefs = {
+    'web': ['web1', 'web2', 'web3'],
+    'db': ['db1', 'db2']
+}
+
+def cd_example():
+    with cd('/tmp'):
+        run('pwd')
+
+
+def push_anyway():
+    with settings(warn_only=True):
+        # simulate failure
+        local('false')
+    run('echo doing it anyway')