Update Plugin documentation for log collector

Change-Id: Ice428db85f8a9f1c7d34e5b1affeeeb0948c3a45
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/ffdc/docs/plugin.md b/ffdc/docs/plugin.md
index 4c20fd9..86c0ab8 100644
--- a/ffdc/docs/plugin.md
+++ b/ffdc/docs/plugin.md
@@ -79,7 +79,7 @@
 
 To accept multiple return values by using coma  "," separated statement
 ```
-     -plugin_name:  return_value1,return_value2 = plugin.foo_func.print_vars
+     - plugin_name:  return_value1,return_value2 = plugin.foo_func.print_vars
 ```
 
 ### Plugin execution output for sample
@@ -97,3 +97,22 @@
         return: 1
         [PLUGIN-END]
 ```
+
+### Plugin FILES Direcive
+
+Rules:
+
+If in the YAML with Plugin module called and corresponding file order
+
+plugin response if there is any will be written to named file, if
+
+```
+    FILES:
+        -'name_file.txt'
+```
+
+Else, plugin response will be skipped and not written to any file.
+```
+    FILES:
+        - None
+```