READMEに無効化設定方法を設定

README.md

@@ -10,7 +10,6 @@ Unofficial script for wakatime tracking in the fish shell.
 - Use git information to determine project name.
 - Can be installed as a [fisher](https://github.com/jorgebucaran/fisher) plugin.
 
-
 ## Getting Started
 
 ### Prerequisites
@@ -34,13 +33,22 @@ If it does not work, please refer to the [official documentation](https://github
 curl -sL https://git.io/fisher | source && fisher install jorgebucaran/fisher
 ```
 
-
 ### Installation
 
 ```fish
 fisher install ik11235/wakatime.fish
 ```
 
+### Disable by environment variable
+
+If you want to disable this plugin temporarily,
+or if you want to use a common config on multiple machines and disable it on only some machines,
+set the following environment variables.
+
+```bash
+export FISH_WAKATIME_DISABLED=true
+```
+
 ## Licence
 
 [MIT](LICENSE)