Extend system.file with file.decode module

Prod-related: PROD-27795(PROD:27795)

Change-Id: I58e15c7c22934da9626fa9ad4de4295956b9daf9
diff --git a/README.rst b/README.rst
index 9655d5e..c844aef 100644
--- a/README.rst
+++ b/README.rst
@@ -519,6 +519,19 @@
               foo: 1
               bar: 'bar'
 
+Ensure presence of file to be decoded through file.decode module (see:
+https://docs.saltstack.com/en/latest/ref/states/all/salt.states.file.html#salt.states.file.decode):
+
+.. code-block:: yaml
+
+    linux:
+      system:
+        file:
+          /tmp/test4.txt:
+            decode: True
+            encoded_data: |
+              dGVzdDQK
+
 Kernel
 ~~~~~~