README.md: Update Type supported types

Currently supported types are `Average`, `Maximum`, `Minimum`, `Sum`
and `ModifiedMedian`.

Change-Id: I0c262fdb1564987a1a4f559cc8a7389022a48c3c
Signed-off-by: George Liu <liuxiwei@ieisystem.com>
diff --git a/README.md b/README.md
index c3da89d..78a4cd8 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@
 ```
 
 Sensors added this way can only use a set of restricted calculations. Currently
-the only type supported is `modifiedMedian`.
+supported types are `Average`, `Maximum`, `Minimum`, `Sum` and `ModifiedMedian`.
 
 The virtual sensor configuration information needs to be added into the relevant
 hardware configuration file in entity-manager. This method of adding a virtual