Add note about multiple processes

sindresorhus#146

readme.md

@@ -4,6 +4,9 @@
 
 All you have to care about is what to persist. This module will handle all the dull details like where and how.
 
+**It does not support multiple processes writing to the same store.**\
+I initially made this tool to let command-line tools persist some data.
+
 *If you need this for Electron, check out [`electron-store`](https://github.com/sindresorhus/electron-store) instead.*
 
 ## Install