Add bruuuh sound to README.md

[Danila Gornushko]

Adding bruuuh sound to demo.mp4 in README.md will significantly improve the satisfaction level of potential users of the extension. Using this sound is a well known pattern for improving the quality of memes. It can also provide a continuous integration (CI) of the meme to dev community.
Link to the resource BRUUUUH

[Полина]

sure

[Maksim Yarkov]

Video has no sound 😥😓😭