Change env vars to match Gerrit Trigger Jenkins plugin

Clarification about password in docs.

README.md

@@ -17,10 +17,11 @@ Latest version from master can be installed by running: `go get github.com/heppu
 go-review uses following environment variables to access gerrit review server:
 
 - `GERRIT_REVIEW_URL`: required
-- `GERRIT_CHANGE_ID`: required
-- `GERRIT_PATCHSET_REVISION`: required
+- `GERRIT_CHANGE_NUMBER`: required
+- `GERRIT_PATCHSET_NUMBER`: required
 - `GERRIT_USERNAME`: optional
-- `GERRIT_PASSWORD`: optional
+- `GERRIT_PASSWORD`: optional - This is the HTTP Credential, not the password
+  used to login to gerrit.
 
 Behavior can be controlled with following flags:
 

cmd/go-review/main.go

@@ -30,8 +30,8 @@ func main() {
 	}
 
 	reviewURL := parseEnv("GERRIT_REVIEW_URL", true)
-	changeID := parseEnv("GERRIT_CHANGE_ID", true)
-	revision := parseEnv("GERRIT_PATCHSET_REVISION", true)
+	changeID := parseEnv("GERRIT_CHANGE_NUMBER", true)
+	revision := parseEnv("GERRIT_PATCHSET_NUMBER", true)
 	username := parseEnv("GERRIT_USERNAME", false)
 	password := parseEnv("GERRIT_PASSWORD", false)