Docker: Example command

[scovetta]

I think the ordering of the docker run command in the README needs to be fixed. At least on Windows, if I have the image name before the environment vars, they don't seem to get passed into the container:

PS D:\temp\codeql-container> docker run --rm codeql:latest -v D:\ReferenceSource\libpng:/opt/src -v d:\temp\codeql-container\results:/opt/results --env CODEQL_CLI_ARGS="database create --language=cpp /opt/src/source_db2"
[2020-07-20 15:09:07,152] INFO: No valid argument passed in for codeql-cli, nothing to do. To perform some task, please set the CODEQL_CLI_ARGS environment variable to a valid argument...

PS D:\temp\codeql-container> docker run --rm -v D:\ReferenceSource\libpng:/opt/src -v d:\temp\codeql-container\results:/opt/results --env CODEQL_CLI_ARGS="database create --language=cpp /opt/src/source_db3" codeql:latest
Initializing database at /opt/src/source_db3.

[jacobmsft]

fixed