Finally add a readme (#123)

* Finally add readme

README.md

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+# LegacyClonk
+
+![Logo](planet/Graphics.c4g/Logo.png)
+
+LC (short for LegacyClonk) is a fan project based on Clonk Rage.
+LegacyClonk continues to receive updates and ensures compatibility with existing Clonk Rage content.
+
+The goal is to fix as many bugs and inelegances as possible, improving quality-of-life and adding nice-to-have features while not impacting the gameplay we’re all used to.
+
+## Installation
+Please refer to the [English](https://clonkspot.org/lc-en#installation-1) or [German](https://clonkspot.org/lc#installation-1) installation manual if you simply want to play the game.
+
+[clonkspot.org](https://clonkspot.org) hosts the community forum, content developer documentation and masterserver.
+
+## Compiling - Quick Start
+**Disclaimer**: This readme is fairly new and may contain mistakes. In case of problems [reach out](#Contact). Readme improvement PRs are welcome.
+
+Essential dependencies:
+- CMake
+- Fairly modern C++ compiler
+	- Windows: **Latest MSVC**
+	- Linux: **g++ ≥ 14.1** or **clang++ ≥ 18.1**
+	- macOS: **open source clang++ ≥ 18.1** - e.g. `brew install llvm@18 ninja`
+- Make or Ninja
+
+Extract the [latest pre-built dependencies](https://github.com/legacyclonk/deps/releases/latest) for your platform into a folder called `deps`.
+Make sure that besides the `CMakeLists.txt` of LegacyClonk there are folders `deps/include`, `deps/lib`, etc. as extracted from the binary package.
+
+
+### Configuring and compiling the engine
+Open a Terminal and navigate to the repository root, such that `CMakeLists.txt` is in the current directory.
+
+#### Windows
+Open the CMake project using Visual Studio.
+
+#### Linux
+Configure with CMake
+```bash
+cmake . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DWITH_DEVELOPER_MODE=ON
+```
+
+Compile with CMake
+```bash
+cmake --build build
+```
+
+#### macOS
+Configure with CMake (FIXME: Rename toolchain file, the version number doesn’t matter)
+```bash
+cmake . -B build -DCMAKE_TOOLCHAIN_FILE=$PWD/autobuild/clang16_mac.cmake
+```
+
+Compile with CMake
+```bash
+cmake --build build
+```
+
+Create the `.app`-bundle
+```bash
+DESTDIR=build/destdir cmake --build build --target install
+```
+
+The `clonk.app` should be generated at `build/destdir/usr/local/clonk.app`.
+
+
+### Setup game folder
+The engine needs various files to run placed next to the engine binary.
+The cleanest way is to create and setup a game folder somewhere outside of the source code repository.
+
+If you want to use an existing game folder (e.g. obtained via the simple binary [Installation](#Installation)) use that folder instead and only do step 2.
+
+1. Create an empty folder at the desired location.
+The guide assumes the directory path to be `~/clonk`.
+1. Create a symbolic link to the binary in the folder
+	- Windows: `New-Item -ItemType Symlink -Path ~/clonk/MyClonk.exe -Target build/clonk.exe` (needs to be run in a terminal with administrator rights)
+	- Linux: `ln -s build/clonk ~/clonk/myclonk`
+	- macOS: `ln -s build/clonk.app ~/clonk/myclonk.app`
+1. Create symbolic links to [Graphics.c4g](planet/Graphics.c4g) and [System.c4g](planet/System.c4g). Without them, the engine won’t start.
+	- Windows
+	```PowerShell
+	New-Item -ItemType Junction -Path ~/clonk/Graphics.c4g -Target planet/Graphics.c4g
+	New-Item -ItemType Junction -Path ~/clonk/System.c4g -Target planet/System.c4g
+	```
+
+	- Linux / macOS
+	```bash
+	ln -s planet/Graphics.c4g planet/System.c4g ~/clonk
+	```
+1. Get official content (optional, but can’t play without some content)
+	- Pre-built: Extract `lc_content.zip` from the [latest release](https://github.com/legacyclonk/content/releases/latest) in the game folder.
+	- From repository
+		1. Clone the content repository in a different folder, e.g. `~/lc_content`: `git clone https://github.com/legacyclonk/content ~/lc_content`
+		2. Create symbolic links for all groups
+			- Windows
+				- Easier: Copy all directories with ending `.c4?`
+				- When planning to edit the content: https://superuser.com/a/1489528
+			- Linux / macOS: `ln -s ~/lc_content/*.c4? ~/clonk`
+
+### Play
+
+- Enter your game folder, e.g. `~/clonk`.
+- Launch `clonk.exe`/`clonk.app`/the `clonk` binary.
+- Enjoy
+
+Remark: In order to join network games with other players (who use release binaries) your `System.c4g` needs to match the one from the host. It can be obtained from [Releases](https://github.com/legacyclonk/LegacyClonk/releases/latest).
+
+## Contact
+
+- IRC: [irc://irc.euirc.net/#legacyclonk](irc://irc.euirc.net/#legacyclonk)
+- Discord: [Server](https://discord.gg/km58ETK)
+- Forum: [https://forum.clonkspot.org](https://forum.clonkspot.org)