chore: Improve installation instructions

Author: Oliver Weiler

README.md

@@ -5,7 +5,7 @@
 
 > Tired of repeatedly typing `cd ..` to walk up the directory tree? Fed up with defining aliases to jump to the first, second or nth parent directory? `up` to the rescue!
 
-up is a tiny shell function which lets you to jump to a parent directory by its name.
+up is a tiny shell function which lets you jump to a parent directory by its name.
 
 ## :sparkles: Features
 
@@ -15,19 +15,30 @@ up is a tiny shell function which lets you to jump to a parent directory by its
 
 ## :gear: Installation
 
-### git + Bash
+### git & Bash
 
-1. Clone the git repository
+Clone `up`'s git repository.
 
 ```sh
 git clone https://github.com/helpermethod/up ~/.up
 ```
 
-2. Add the following line to your `.bashrc` (Linux) or `.bash_profile` (macOS)
+Add the following line to your `.bashrc` (Linux) or `.bash_profile` (macOS) to install `up`.
 
 ```sh
 . "$HOME/.up/up"
 ```
 
+Add the following line to your `.bashrc` (Linux) or `.bash_profile` (macOS) to enable `up`'s Bash completion.
+
+```sh
+. "$HOME/.up/completion/bash/up"
+```
+
+### git & zsh
+
+TBD
+
 ## Usage
 
+TBD