task: adding more doc on the README

[paganotoni]

What is being done in this PR?

This PR adds a bit of documentation in the two larger features Visho has: Highlight and snippets. I changed the README document to include that. It also adds a new Visho logo.

What are the main choices made to get to this solution?

Decided to use the preview image we have on top to illustrate the syntax highlight. We could later on go into more detail.

List the manual test cases you've covered before sending this PR:

• Tested the Markdown locally to render the files added. I could check that the highlight image is rendering correctly there. ✅

What was discovered while working on it? (Optional)

Discovered the reason why the preview image was not being shown in the VSCode marketplace and tweaked its URL so it works. I used the same technique to specify the Visho logo in the package.json and in the README.

[paganotoni]

@YanDeLeon merged this one as it's only docs. LMK if you find issues you think we should solve. I want to get quickly to the store to confirm images are loading.

[YanDeLeon]

Only one little thing. The PL option of the snippets is only for the old ones. The new ones are only with the p .

PS. Love the logo. Do you think we should mention DALL-E ?

@paganotoni the build failed. I think we need to add an icon for plush files or use the html one