diff --git a/README.md b/README.md
index 13776c7..2d0a903 100644
--- a/README.md
+++ b/README.md
@@ -2,14 +2,17 @@
 
 ## Requirements
 
-* lua
+* lua >= 5.3
 * curl
 * sed
 * date
 
 ## Usage
 
-    c4mate [-u <user>] [ <query> | -b <id> | -l | +/-<amount> | -g <amount> <user> [<reason>]]
+If no username is given via the "-u" command line flag, c4mate will use the
+value of the $USER environment variable as username.
+
+    Usage: c4mate [-u <user>] [ <query> | -b <id> | -l | +/-<amount> | -g <amount> <user> [<reason>]]
     Display current balance:
         c4mate
     Find and buy item (interactive):