Added sample :Gof command to README ✨

Hmm, I uploaded :Gof screen capture to imgur, the image appears in the imgur site but direct link to gif does not show the image 🤔
https://imgur.com/dJ8ypKT

I registered imgur and uploaded (I uploaded the previous images from free account (not logged-in)).
And fixed all image URLs.

@mattn How do you think? Is there plan to merge?

I think -T should need to be changed, because prefix is for call of terminal-api, but currently drop is used.

• change -T [prefix] to -tf [funcname]
• add -tc ["call" or "drop"]

so we can send ["call","[funcname]","[filename]"] or ["drop","[filename]"]

Or, -tc {command} is not necessary because currently Vim terminal API only supports call or drop.

• change -T [prefix] to -tf [funcname]
• if -tf option was given, send ["call","[funcname]","[filename]"]. otherwise ["drop","[filename]"]

Done edc392f

LGTM, Thank you