Add dependency suggestions (#78)

Don’t require kevinrob/guzzle-cache-middleware in GuzzleFeatureRequester

Author: arun251

composer.json

@@ -26,10 +26,10 @@
         "predis/predis": "^1.0",
         "zendframework/zend-serializer": "^2.7"
     },
-    "suggested": {
-        "guzzlehttp/guzzle": "^6.2.1",
-        "kevinrob/guzzle-cache-middleware": "^1.4.1",
-        "predis/predis": "^1.0"
+    "suggest": {
+        "guzzlehttp/guzzle": "(^6.2.1) Required when using the default FeatureRequester",
+        "kevinrob/guzzle-cache-middleware": "(^1.4.1) Recommended for performance when using the default FeatureRequester",
+        "predis/predis": "(^1.0) Required when using LDDFeatureRequester"
     },
     "autoload": {
         "psr-4": {