SECURITY-9850: update README.md

Co-authored-by: Krisztian Nagy <krisztian.nagy@emarsys.com>

README.md

@@ -1,4 +1,4 @@
-EscherRuby - HTTP request signing lib [![Build Status](https://travis-ci.org/emartech/escher-ruby.svg?branch=master)](https://travis-ci.org/emartech/escher-ruby)
+EscherRuby - HTTP request signing lib [![Build Status](https://img.shields.io/github/actions/workflow/status/emartech/escher-ruby/ruby.yml?branch=master)](https://github.com/emartech/escher-ruby/actions/workflows/ruby.yml)
 =====================================
 
 Escher helps you creating secure HTTP requests (for APIs) by signing HTTP(s) requests. It's both a server side and client side implementation. The status is work in progress.
@@ -11,6 +11,12 @@ Check out a [working example] (https://github.com/emartech/escher-ruby-example).
 
 ### Local development
 
+To ensure you have all submodules (including test suites), please clone the repository with the `--recursive` flag:
+
+```bash
+git clone --recursive https://github.com/emartech/escher-ruby.git
+```
+
 #### Running tests
 
 ```bash