Document building and installing in the README (#23)

* added installation and building from source info to readme

* wip disclaimer

* Update README.md

totally knew this was a thing

Co-authored-by: Florian Sihler <florian.sihler@uni-ulm.de>

* document slicing and GitHub Releases

* recommend gh releases install

* added splash image

---------

Co-authored-by: Florian Sihler <florian.sihler@uni-ulm.de>

README.md

@@ -1,18 +1,51 @@
 # vscode-flowr
-flowR Extension for Visual Studio Code 
+*flowR* Extension for Visual Studio Code. For more information on *flowR*, check out [the main repository](https://github.com/Code-Inspect/flowr).
 
-## Features
-TO DO
+![A screenshot of the extension being used to reconstruct a slice](media/splash.png)
 
-## Requirements
-TO DO
+**This extension is still work in progress, as is this README. Please stay tuned for cool features and cooler documentation!**
 
-## Extension Settings
-TO DO
+## Installing
 
-# Developing
+### From Visual Studio Marketplace
+vscode-flowr is not available on the Visual Studio Marketplace yet. For now, we recommend installing from GitHub Releases, or building from source.
 
-## Git Hooks
+### From GitHub Releases
+You can find official releases of the extension in the [Releases](https://github.com/Code-Inspect/vscode-flowr/releases) section of the repository. Simply select the version you'd like to download, open up the Assets section at the bottom, and download the `vscode-flowr-[version].vsix` contained in it.
+
+From Visual Studio Code, open the Extensions tab and click on the three dots in the top right to select "Install from VSIX..." Alternatively, you can use the Command Palette to select the option directly. Then, you can select the `vsix` file you downloaded to install it.
+
+### From build artifacts
+You can easily download the most recent build of the extension by heading to the [Actions tab](https://github.com/Code-Inspect/vscode-flowr/actions/workflows/package.yml), where you will find a list of runs. Selecting the most recent run will display a summary of it, at the bottom of which you can find the Artifacts section and the `Extension vsix` artifact. Download it und unzip it.
+
+Then, you can install it the same way as you would the `vsix` downloaded [from GitHub Releases](#from-github-releases).
+
+## Using
+
+We recommend using the [R extension](https://marketplace.visualstudio.com/items?itemName=REditorSupport.r) for Visual Studio Code in addition to this extension. For more information on R development in Visual Studio Code, you can also check out [this helpful article](https://code.visualstudio.com/docs/languages/r).
+
+### Slicing
+You can generate a [slice](https://github.com/Code-Inspect/flowr/wiki/Terminology#program-slice) of the currently highlighted variable in any R code by using the "Slice for Cursor Position" command. All code that is not part of the generated slice will then be grayed out.
+
+To clear the slice highlighting, use the "Clear Slice Presentation" command.
+
+You can also reconstruct a piece of code based on the slice of a variable by using the "Slice for Cursor Position (Reconstruct)" command. The reconstructed code will be opened in a new file.
+
+## Developing
+
+### Building and running from source
+After cloning the repository, required dependencies can be installed using [npm](https://www.npmjs.com/):
+```
+npm ci
+```
+
+Opening the cloned repository in Visual Studio Code allows using the [existing launch configurations](https://github.com/Code-Inspect/vscode-flowr/blob/main/.vscode/launch.json) which can launch Visual Studio Code with the extension enabled. To use them, open the Run and Debug view and press the Run button at the top, or use the <kbd>F5</kbd> shortcut to start debugging.
+
+You can then open the [example folder](https://github.com/Code-Inspect/vscode-flowr/tree/main/example) contained in this repository to try out the extension for yourself.
+
+To build the extension into a `vsix` file, see [this documentation article](https://code.visualstudio.com/api/working-with-extensions/publishing-extension).
+
+### Git hooks
 This repository contains some git hooks to ensure that linting and other actions happen. Register these hooks by running:
 ```sh
 git config core.hooksPath .githooks