Updated README to reflect proper usage of --project_id flag

[jdwall]

Updated README to reflect proper usage of --project_id flag when loading data. I am not entirely sure why it is only with bq load that you have to use --project_id= yet the rest of the times bq uses --project=

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[jdwall]

I signed it!

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CLAs look good, thanks!

[jdwall]

No problem, it was a simple change! Have a great start to the work week, @tedsta!