Clean up the README file

Adds documentation regarding how to customize the output, as well as phix
the phormatting.

README.md

@@ -1,11 +1,21 @@
 <h2 align="center">fet.sh</h1>
 
-Installing:
- Arch: fet.sh-git (AUR)
- Other Distros: copy 'fet.sh' to somewhere in $PATH
-
 <div align="center">
 fetch written in POSIX shell with no external commands
 <br>
 <img src="screenshot.png" width="250px">
 </div>
+
+
+### Installing
+  **Arch:** [fet.sh-git](https://aur.archlinux.org/packages/fet.sh-git/) (AUR)  
+  **Other Distros:** copy `fet.sh` to somewhere in $PATH
+
+### Customization
+`fet.sh` can be configured using environment variables, for example:
+```sh
+$ separator=" > " fet.sh
+```
+Supported options are:
+- `accent`
+- `separator`