docs(readme): add Arch Linux installation instructions (#22)

Co-authored-by: Markus Unterwaditzer <[email protected]>

Author: adamperkowski

README.md

@@ -33,7 +33,13 @@ common commands (`yarn`, `npm`, `node`).
 
 ## Installation
 
-[Download the latest binary](https://github.com/untitaker/quickenv/releases) and:
+Install quickenv:
+
+* [from GitHub](https://github.com/untitaker/quickenv/releases) as a standalone binary
+* [from AUR for ArchLinux](https://aur.archlinux.org/packages/quickenv), e.g. `paru -S quickenv`
+* [or build from source](#ref-build-from-source)
+
+Then set it up in your shell:
 
 ```bash
 # Into your bashrc/zshrc. This should be at the front of your PATH, such that
@@ -55,7 +61,9 @@ Some notes:
 
 * `quickenv` assumes a POSIX environment.
 
-### Installation from source
+<a name=ref-build-from-source></a>
+
+### Building from source
 
 ```bash
 cargo install quickenv  # latest stable release