Update README - add handlebars-rust in the Wild

[Binlogo]

Before creating a pull-request, please check https://github.com/handlebars-lang/handlebars.js/blob/master/CONTRIBUTING.md first.

Generally we like to see pull requests that

• Please don't start pull requests for security issues. Instead, file a report at https://www.npmjs.com/advisories/report?package=handlebars
• Maintain the existing code style
• Are focused on a single change (i.e. avoid large refactoring or style adjustments in untouched code if not the primary goal of the pull request)
• Have good commit messages
• Have tests
• Have the typings (types/index.d.ts) updated on every API change. If you need help, updating those, please mention that in the PR description.
• Don't significantly decrease the current code coverage (see coverage/lcov-report/index.html)
• Currently, the 4.x-branch contains the latest version. Please target that branch in the PR.

[jaylinski]

As far as I know, we only document things in this section that use the handlebars-js library from this repo.

Other languages are documented here: https://handlebarsjs.com/installation/#other-programming-languages

But I think we should add a "Other programming languages"-section in the README too.

I'll keep this PR open and will think about it.

[Binlogo]

Thank you for your information. Documenting other programming languages can help users of different backgrounds get started quickly.