README: Update Type for D-Bus config

According to entity-manager schema, the first M of ModifiedMedian
should be capitalized. Also adds a hyperlink to the schema.

Tested:
Configure phosphor-virtual-sensor with "Type": "ModifiedMedian", the
sensor defined in entity-manager json is exposed successfully.

Change-Id: I90fa91d3c45e24914610245eec43dd2924957855
Signed-off-by: Jiaqing Zhao <jiaqing.zhao@intel.com>
diff --git a/README.md b/README.md
index 60c4df0..0e5bb38 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,7 @@
 {
   "Desc": {
     "Config": "D-Bus",
-    "Type": "modifiedMedian"
+    "Type": "ModifiedMedian"
   }
 }
 ```
@@ -31,4 +31,4 @@
 
 The virtual sensor configuration in entity manager follows a different format
 to the JSON in virtual_sensor_config.json (specified in
-entity-manager/schemas/VirtualSensor.json).
+[entity-manager/schemas/VirtualSensor.json](https://github.com/openbmc/entity-manager/blob/master/schemas/VirtualSensor.json)).