Merge pull request #247 from Flow-Launcher/update_readme_usage

Update plugin usage in README

Author: jjw24

README.md

@@ -45,7 +45,7 @@ Windows may complain about security due to code not being signed, this will be c
 - Open flow's search window: <kbd>Alt</kbd>+<kbd>Space</kbd> is the default hotkey.
 - Open context menu: <kbd>Ctrl</kbd>+<kbd>O</kbd>/<kbd>Shift</kbd>+<kbd>Enter</kbd>.
 - Cancel/Return to previous screen: <kbd>Esc</kbd>.
-- Install/Uninstall plugins: in the search window, type `wpm install/uninstall` + the plugin name.
+- Install/Uninstall/Update plugins: in the search window, type `pm`/`pm uninstall`/`pm update` + the plugin name.
 - Saved user settings are located:
   - If using roaming: `%APPDATA%\FlowLauncher`
   - If using portable, by default: `%localappdata%\FlowLauncher\app-<VersionOfYourFlowLauncher>\UserData`