Add help

configure

@@ -1,5 +1,18 @@
 #!/bin/sh
 
+if [[ "$*" == *"--help"* ]] || [[ "$*" == *"-h"* ]]
+then
+    echo "Use environment variables to pass values:
+    CC      - compiler (default: cc)
+    CFLAGS  - flags for compiler
+    LDFLAGS - flags for linker
+    OUT     - out file (default: game
+    SIZE    - size of game field
+    DEFX    - start x
+    DEFY    - start y"
+    exit 1
+fi
+
 CC=${CC:-cc}
 RM=${RM:-rm -f}
 CFLAGS=${CFLAGS:-}