Add Go Report Card and Slack Status badges to README.md (#177)

Author: roger2hk

README.md

@@ -1,5 +1,8 @@
 # SCTFE
 
+[![Go Report Card](https://goreportcard.com/badge/github.com/transparency-dev/static-ct)](https://goreportcard.com/report/github.com/transparency-dev/static-ct)
+[![Slack Status](https://img.shields.io/badge/Slack-Chat-blue.svg)](https://transparency-dev.slack.com/)
+
 This personality implements [CT Static API](https://c2sp.org/static-ct-api) 
 using [Trillian Tessera](https://github.com/transparency-dev/trillian-tessera) 
 to store data. It is based on