install-by-docker: fix curl command for Windows compatibility

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

container-deployment/install-by-docker.md

@@ -75,9 +75,11 @@ $ docker run -p 9880:9880 -v $(pwd)/tmp:/fluentd/etc fluent/fluentd:edge-debian
 Use `curl` command to post sample logs via HTTP like this:
 
 ```text
-$ curl -X POST -d 'json={"json":"message"}' http://127.0.0.1:9880/sample.test
+$ curl -X POST -d "json={\"json\":\"message\"}" http://127.0.0.1:9880/sample.test
 ```
 
+(Note: For Windows users, it is recommended to run this command in Command Prompt (cmd.exe). If using PowerShell, the JSON string may require different escaping rules to be parsed correctly.)
+
 Use `docker ps` command to retrieve container ID and use `docker logs` command to check the specific container's log like this:
 
 ```text