SCB-378 update saga demo readme to fix docker-compose.yml file path

[lijasonvip]

Signed-off-by: lijasonvip libo75@huawei.com

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a JIRA issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes.
• Each commit in the pull request should have a meaningful subject line and body.
• Format the pull request title like [SCB-XXX] Fixes bug in ApproximateQuantiles, where you replace SCB-XXX with the appropriate JIRA issue.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Run mvn clean install to make sure basic checks pass. A more thorough check will be performed on your pull request automatically.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

---

[coveralls]

Coverage increased (+0.1%) to 95.066% when pulling 8125a6e on lijasonvip:readme-fix into 4e8a3e2 on apache:master.