A picture is worth 1000 words. Working with github repos, sometimes you want to include a screenshot in your repos. Today I'll help you getting this done in one step.
Go to your repo page and click on issues.
Click new issue
Take a screenshot you wanna add and paste it there using Control + V or whatever you like.
You will get a link once the screenshot is uploaded. Just copy it and paste it in your README.md
Close the page 'new issue', you don't need to create an issue.
Commit and push changes. Done.