Add installation instructions for all platforms

INSTALL.md

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+# Setting Up Zoo Modeling App
+
+Compared to other CAD software, getting Zoo Modeling App up and running is quick and straightforward across platforms. It's about 100MB to download and is quick to install.
+
+## Windows
+
+1. Download the [Zoo Modeling App installer](https://zoo.dev/modeling-app/download) for Windows and for your processor type.
+
+2. Once downloaded, run the installer `Zoo Modeling App-{version}-{arch}-win.exe` which should take a few seconds.
+
+3. The installation happens at `C:\Program Files\Zoo Modeling App`. A shortcut in the start menu is also created so you can run the app easily by clicking on it.
+
+## macOS
+
+1. Download the [Zoo Modeling App installer](https://zoo.dev/modeling-app/download) for macOS and for your processor type.
+
+2. Once downloaded, open the disk image `Zoo Modeling App-{version}-{arch}-mac.dmg` and drag the applications to your `Applications` directory.
+
+3. You can then open your `Applications` directory and double-click on `Zoo Modeling App` to open.
+
+
+## Linux 
+
+1. Download the [Zoo Modeling App installer](https://zoo.dev/modeling-app/download) for Linux and for your processor type.
+
+2. Install the dependencies needed to run the [AppImage format](https://appimage.org/).
+    -  On Ubuntu, install the FUSE library with these commands in a terminal.
+       ```bash
+       sudo apt update
+       sudo apt install libfuse2
+       ```
+    - Optionally, follow [these steps](https://github.com/probonopd/go-appimage/blob/master/src/appimaged/README.md#initial-setup) to install `appimaged`. It is a daemon that makes interacting with AppImage files more seamless. 
+    - Once installed, copy the downloaded `Zoo Modeling App-{version}-{arch}-linux.AppImage` to the directory of your choice, for instance `~/Applications`.
+
+   - `appimaged` should automatically find it and make it executable. If not, run:
+     ```bash
+     chmod a+x ~/Applications/Zoo\ Modeling\ App-{version}-{arch}-linux.AppImage
+     ```
+
+3. You can double-click on the AppImage to run it, or in a terminal with this command:
+   ```bash
+    ~/Applications/Zoo\ Modeling\ App-{version}-{arch}-linux.AppImage
+   ```