Use XDG base directory spec (#93)

* Use XDG base directory spec

* update other installation path

* Add comments

* re-apply Kai's changes

* Describe both system-wide and user-specific installations

---------

Co-authored-by: Hendrik Cannoodt <hendrik.cannoodt@gmail.com>
Co-authored-by: Toni Verbeiren <toni.verbeiren@gmail.com>

installation/index.qmd

@@ -140,10 +140,14 @@ You can choose to install `default-jdk` instead of the more explicit `openjdk-17
 
 ## Linux
 
-To install Viash to a `bin` folder in your current directory, run the following command to download and run the install script:
+To install Viash to a `bin` folder on your PATH, run the following command to download and run the install script:
 
 ```bash
-wget -qO- dl.viash.io | bash; mv viash $HOME/bin
+wget -qO- dl.viash.io | bash
+```
+
+```bash
+sudo mv viash /usr/local/bin
 ```
 
 To verify your installation, run the following command:
@@ -154,12 +158,32 @@ viash --help
 
 ## macOS
 
-To install Viash to a `bin` folder in your current directory, run the following command to download and run the install script:
+Viash can be easily installed in the working directory by running the following command:
 
 ```bash
-curl -fsSL dl.viash.io | bash; mv viash $HOME/bin
+curl -fsSL dl.viash.io | bash
 ```
 
+This will download the Viash binary to the current working directory and make it executable.
+
+Next, the Viash executable can be moved to either a system location (`/usr/local/bin`) or a user location (`~/bin`):
+
+1. To install the Viash executable to `/usr/local/bin`, simply run:
+
+    ```bash
+    sudo mv viash /usr/local/bin
+    ```
+
+    Please note that `sudo` rights are required.
+
+2. To install Viash to the `$HOME/bin` folder, run the following command instead:
+
+    ```bash
+    mv viash $HOME/bin/viash
+    ```
+
+    Make sure to create the `~/bin` directory if it doesn't exist yet and add `~/bin` to the `$PATH` environment variable in your shell.
+
 To verify your installation, run the following command:
 
 ```bash
@@ -168,10 +192,14 @@ viash --help
 
 ## Windows
 
-To install Viash to a `bin` folder in your current directory, run the following command to download and run the install script:
+To install Viash to a `bin` folder on your PATH, run the following command to download and run the install script:
+
+```bash
+wget -qO- dl.viash.io | bash
+```
 
 ```bash
-wget -qO- dl.viash.io | bash; mv viash $HOME/bin
+sudo mv viash /usr/local/bin
 ```
 
 To verify your installation, run the following command: