docs(#5): minimal readme & contributing

CONTRIBUTING.md

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+# Contributing to Vivify
+
+Contributions are very welcome! If you would like to contribute, please make
+sure you follow the steps below:
+
+- Make sure there is an issue corresponding to what you are working on
+- Use [conventional commits](https://www.conventionalcommits.org/en/v1.0.0/)
+  with `#<your issue number>` as the context for all commits
+- Make sure you are not adding any merge commits to your branch
+- Open a pull request & wait for a review!🩵

README.md

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+# Vivify
+
+Vivify brings your (Markdown) files to life in the browser!
+
+## Features
+
+- various [Markdown features](#markdown)
+- links to other files: [relative links like in
+  GitHub](https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#relative-links)
+  as well as absolute file links
+- view non-markdown files with code syntax highlighting
+- view & navigate directories, hidden "back to parent directory" button at the
+  top-left of the file viewer
+- easy to integrate with any editor for live synchronization (see [editor
+  support](#editor-support))
+- Vivify server starts lazily and automatically shuts down when no more viewers
+  are connected
+
+### Markdown
+
+- heading/anchor links
+- GitHub emojis `:smile:`
+- full Katex math support
+- GitHub task-lists
+- syntax highlighting for code
+
+If you need any additional features, feel free to [open an
+issue](https://github.com/jannis-baum/vivify/issues/new/choose) or
+[contribute](CONTRIBUTING.md)!
+
+## Usage
+
+- download & unpack the latest release for your system (macOS or Linux)
+- add the two executables to your `$PATH`
+- run `viv <file>` to view `<file>`
+
+## Editor Support
+
+Vivify has a simple API to integrate your favorite editor so the viewer live
+updates to any changes as you are typing and the scrolling is smoothly
+synchronized!
+
+See below for a list of existing editor plugins. In case your favorite editor is
+not yet supported, use these as an example to write your own and add it to the
+list!
+
+### Existing integration
+
+- for Vim: [vivify.vim](https://github.com/jannis-baum/vivify.vim)
+
+## Get help
+
+Is something not working or do you have any questions? [Open an
+issue](https://github.com/jannis-baum/vivify/issues/new/choose)!
+
+## Acknowledgments
+
+I have been using
+[iamcco/markdown-preview.nvim](https://github.com/iamcco/markdown-preview.nvim)
+for the longest time and started this project because
+
+1. I wanted a Markdown viewer that works without Vim and
+2. I wanted a Markdown viewer that supports file links like in GitHub.
+
+Looking at
+[iamcco/markdown-preview.nvim](https://github.com/iamcco/markdown-preview.nvim)
+helped in development, particularly with regard to which `npm` packages to use.