fix(readme): update installation

i remembered cargo will install from git

README.md

@@ -1,10 +1,13 @@
 # git-su
+
 switch between git users.
 
 is this original? not at all. this is my own take on it because i wanted my own syntax for the cli.
 
 ## usage
+
 note: git allows running commands formatted in `git-*` as `git *`, so you can also run this as `git su`.
+
 ```
 Usage: git-su <COMMAND>
 
@@ -23,7 +26,11 @@ Options:
 
 ## installation
 
-there is currently no automated installation. simply build the program and place the resulting executable in your path.
+install using cargo.
+
+```
+cargo install cargo install --git https://git.ozzy.top/ozzy/git-su
+```
 
 ## building