docs: add Google Cloud Samples browser link to readme template

[msampathkumar]

Adding a generic Google Code Sample link to the readme template.

This is for the benefit of the users, in navigating available Google Cloud code samples.

Fixes #issue

It's a good idea to open an issue first for discussion.

• I have followed Sample Format Guide
• pom.xml parent set to latest shared-configuration
• Appropriate changes to README are included in PR
• API's need to be enabled to test (tell us)
• Environment Variables need to be set (ask us to set them)
• Tests pass: mvn clean verify required
• Lint passes: mvn -P lint checkstyle:check required
• Static Analysis: mvn -P lint clean compile pmd:cpd-check spotbugs:check advisory only
• Please merge this PR for me once it is approved.