How to upload a measure to BCL?

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I have created a measure that I want to publish. The BCL describes a 4-step process to contribute data here. I am having trouble with the first step: 'initialize a new extension gem'. As I am not familiar with gems, can anyone explain or point me to a tutorial? For now, I only have my measure folder. Through my research, I understand that publishing measures was done by compressing the measure folder into zip and uploading to BCL, is that still possible?