docs(readme): update the README.md file

Author: sandr01d

README.md

@@ -177,6 +177,9 @@ daemonize = true
 # Maximum number of clips in history.
 max_history = 50
 
+# Clears the history on startup when set to true
+clear_history_on_start = false
+
 # File path for clip history.
 # If this value is omitted, `clipcatd` will persist history in `$XDG_CACHE_HOME/clipcat/clipcatd-history`.
 history_file_path = "/home/<username>/.cache/clipcat/clipcatd-history"