Add demo-api readme

Author: camilamaia

demo-api/README.md

@@ -0,0 +1,18 @@
+# Demo API
+
+[Demo API](https://github.com/scanapi/demo-api) is an API created by the ScanAPI team for demo
+purposes. It can be accessed at https://demo.scanapi.dev/api
+
+Requirements:
+- [ScanAPI](https://pypi.org/project/scanapi/)
+
+# Run
+
+```shell
+$ git clone git@github.com:scanapi/examples.git
+$ cd demo-api
+$ source .env
+$ scanapi
+```
+
+The report will be available at `scanapi-report.html`