Ability to get file from secured source

PROD-31387

Change-Id: Ica1c58f89d962fb4c3a8bc63f207f664ee39c1e5
diff --git a/README.rst b/README.rst
index a14ae15..c315aee 100644
--- a/README.rst
+++ b/README.rst
@@ -546,6 +546,28 @@
           /tmp/test.txt:
             contents_grains: motd
 
+Ensure presence of file by specifying its secured source:
+
+.. code-block:: yaml
+
+    linux:
+      system:
+        file:
+          /tmp/test.txt:
+            secured_source:
+              protocol: http #optional
+              user: foo
+              password: bar
+              url: example.com/test.txt
+            secured_hash: #optional
+              url: example.com/test.txt.md5
+            user: root #optional
+            group: root #optional
+            mode: 700 #optional
+            dir_mode: 700 #optional
+            encoding: utf-8 #optional
+            makedirs: true #optional
+
 Ensure presence of file to be serialized through one of the
 serializer modules (see:
 https://docs.saltstack.com/en/latest/ref/serializers/all/index.html):