[Stdin] Added configuration file documentation

Author: Kirottu

plugins/stdin/README.md

@@ -7,3 +7,15 @@ Allows for easy integration into scripts that have been made with something like
 
 This plugin should generally be used alone, if a dmenu replacement is needed. This can be done with `anyrun --plugins libstdin.so`.
 The content to fuzzy match on needs to be piped into Anyrun.
+
+## Configuration
+
+```ron
+Config(
+  // Whether to allow the user to input any arbitrary text besides the options provided
+  allow_invalid: false,
+  // How many entries should be displayed at max
+  max_entries: 5,
+)
+
+```