Update README for CCMetric

internal/ccMetric/README.md

@@ -12,7 +12,21 @@ type ccMetric struct {
     tm     time.Time         // line-protocol
     meta   []*influx.Tag
 }
+
+type CCMetric interface {
+    influx.MutableMetric        // the same functions as defined by influx.MutableMetric
+    RemoveTag(key string)       // this is not published by the original influx.MutableMetric
+    Meta() map[string]string
+    MetaList() []*lp.Tag
+    AddMeta(key, value string)
+    HasMeta(key string) bool
+    GetMeta(key string) (string, bool)
+    RemoveMeta(key string)
+}
 ```
 
-The `CCMetric` interface provides the same functions as the `MutableMetric` like `{Add, Remove, Has}{Tag, Field}` and additionally provides `{Add, Remove, Has}Meta`
+The `CCMetric` interface provides the same functions as the `MutableMetric` like `{Add, Remove, Has}{Tag, Field}` and additionally provides `{Add, Remove, Has}Meta`.
 
+The InfluxDB protocol creates a new metric with `influx.New(name, tags, fields, time)` while CCMetric uses `ccMetric.New(name, tags, meta, fields, time)` where `tags` and `meta` are both of type `map[string]string`.
+
+You can copy a CCMetric with `FromMetric(other CCMetric) CCMetric`. If you get an `influx.Metric` from a function, like the line protocol parser, you can use `FromInfluxMetric(other influx.Metric) CCMetric` to get a CCMetric out of it (see `NatsReceiver` for an example).