Add httpjson readme

closes #275

plugins/httpjson/README.md

@@ -0,0 +1,69 @@
+# HTTP JSON Plugin
+
+The httpjson plugin can collect data from remote URLs which respond with JSON. Then it flattens JSON and finds all numeric values, treating them as floats.
+
+For example, if you have a service called _mycollector_, which has HTTP endpoint for gathering stats http://my.service.com/_stats:
+
+```
+[[httpjson.services]]
+  name = "mycollector"
+
+  servers = [
+    "http://my.service.com/_stats"
+  ]
+
+  # HTTP method to use (case-sensitive)
+  method = "GET"
+```
+
+The name is used as a prefix for the measurements.
+
+The `method` specifies HTTP method to use for requests.
+
+You can specify which keys from server response should be considered as tags:
+
+```
+[[httpjson.services]]
+  ...
+
+  tag_keys = [
+    "role",
+    "version"
+  ]
+```
+
+**NOTE**: tag values should be strings.
+
+You can also specify additional request parameters for the service:
+
+```
+[[httpjson.services]]
+  ...
+
+ [httpjson.services.parameters]
+    event_type = "cpu_spike"
+    threshold = "0.75"
+
+```
+
+
+# Sample
+
+Let's say that we have a service named "mycollector", which responds with:
+```json
+{
+    "a": 0.5,
+    "b": {
+        "c": "some text",
+        "d": 0.1,
+        "e": 5
+    }
+}
+```
+
+The collected metrics will be:
+```
+httpjson_mycollector_a value=0.5
+httpjson_mycollector_b_d value=0.1
+httpjson_mycollector_b_e value=5
+```

plugins/httpjson/httpjson.go

@@ -62,8 +62,8 @@ var sampleConfig = `
     # HTTP method to use (case-sensitive)
     method = "GET"
 
-    # List of tag names to extract from server response
-    # tagKeys = [
+    # List of tag names to extract from top-level of JSON server response
+    # tag_keys = [
     # 	"my_tag_1",
     # 	"my_tag_2"
     # ]

plugins/httpjson/httpjson_test.go

@@ -35,7 +35,6 @@ const validJSONTags = `
 		"build": "123"
 	}`
 
-
 const invalidJSON = "I don't think this is JSON"
 
 const empty = ""