Change -config.file to --config.file in Readme and error message

README.md

@@ -66,7 +66,7 @@ vendoring feature, so you will also need to set the `GO15VENDOREXPERIMENT=1`
 environment variable in this case:
 
     $ GO15VENDOREXPERIMENT=1 go get github.com/prometheus/prometheus/cmd/...
-    $ prometheus -config.file=your_config.yml
+    $ prometheus --config.file=your_config.yml
 
 You can also clone the repository yourself and build using `make`:
 
@@ -75,7 +75,7 @@ You can also clone the repository yourself and build using `make`:
     $ git clone https://github.com/prometheus/prometheus.git
     $ cd prometheus
     $ make build
-    $ ./prometheus -config.file=your_config.yml
+    $ ./prometheus --config.file=your_config.yml
 
 The Makefile provides several targets:
 

cmd/prometheus/main.go

@@ -362,7 +362,7 @@ func reloadConfig(filename string, logger log.Logger, rls ...Reloadable) (err er
 
 	conf, err := config.LoadFile(filename)
 	if err != nil {
-		return fmt.Errorf("couldn't load configuration (-config.file=%s): %v", filename, err)
+		return fmt.Errorf("couldn't load configuration (--config.file=%s): %v", filename, err)
 	}
 
 	failed := false
@@ -373,7 +373,7 @@ func reloadConfig(filename string, logger log.Logger, rls ...Reloadable) (err er
 		}
 	}
 	if failed {
-		return fmt.Errorf("one or more errors occurred while applying the new configuration (-config.file=%s)", filename)
+		return fmt.Errorf("one or more errors occurred while applying the new configuration (--config.file=%s)", filename)
 	}
 	return nil
 }