Create example to showcase how to upload files

[aluruiz]

This PR's adds an example showcasing how to upload files to VirusTotal using vt-go.

The example program accepts two arguments, apikey and path:

• -apikey: taken from VirusTotal.
• -path: the folder you want the files upload from.

The script outputs the analyses IDs for each uploaded file. The following snippet show the output format:

$ go run main.go -apikey="" path=/mnt/c/Users/Shiri/Desktop/test
Scanning: /mnt/c/Users/Shiri/Desktop/test 
Uploading: /mnt/c/Users/Shiri/Desktop/test/chrome.exe 
ID: YjU1NWNlNjkyNGRlOGIyMjEyMWQyOWE2YTE1M2QzZmE6MTYxNzg4MTI5MA== Type: analysis 
Analysis Status: queued 

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[aluruiz]

@googlebot I signed it!