DOC: README: DeviceAtlas sample configuration updates

Needs to distinguish the convertor and the fetch type samples.
More explanations are made about their specific purposes.
diff --git a/README b/README
index 5ebc141..eb8f139 100644
--- a/README
+++ b/README
@@ -233,8 +233,25 @@
     frontend
 	bind *:8881
 	default_backend servers
-	http-request set-header X-DeviceAtlas-Data %[req.fhdr(User-Agent),da-csv(primaryHardwareType,osName,osVersion,browserName,browserVersion)]
+
+There are two distinct methods available, one which leverages all HTTP headers
+and one which uses only a single HTTP header for the detection. The former
+method is highly recommended and more accurate.
+
+
+All HTTP headers
+
+
+      http-request set-header X-DeviceAtlas-Data %[da-csv-fetch(primaryHardwareType,osName,osVersion,browserName,browserVersion)]
+
+
+Single HTTP header (e.g. User-Agent)
+
+
+      http-request set-header X-DeviceAtlas-Data %[req.fhdr(User-Agent),da-csv-conv(primaryHardwareType,osName,osVersion,browserName,browserVersion)]
+
 
+Please find more information about DeviceAtlas and the detection methods at https://deviceatlas.com/resources .
 
 1.2) 51Degrees Device Detection
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