[Root] Updating README for CloudSqlImportOptimization (#188)
[Root] Updating README for CloudSqlImportOptimization (#188)

* [Root] Updating README with notes about mysqlclient, secure file priv and encoding instructions, and unix support. Also fixing some mispelled commands and breaking up long commands.

* [Root] Updating --secure-file-priv comments with proper notes about using sudo.

GoogleCloudPlatform/pontem,GoogleCloudPlatform/pontem