Update README formatting

plugins/transfer/README.md

-# `transfer.sh` plugin
-transfer.sh is an easy file sharing service from the command line
+# `transfer` plugin
+
+[`transfer.sh`](https://transfer.sh) is an easy to use file sharing service from the command line
 
 ## Usage
-Example
-> transfer file.txt
-> transfer directory/
 
+Add `transfer` to your plugins array in your zshrc file:
+```zsh
+plugins=(... transfer)
+```
+
+Then you can:
+
+- transfer a file:
+
+```zsh
+transfer file.txt
+```
+
+- transfer a whole directory (it will be automatically compressed):
+
+```zsh
+transfer directory/
+```