update README

README.md

@@ -86,17 +86,11 @@ https://github.com/wasabiz/picrin
 
 ## How to use it
 
-- debug-run
-
-	By default make command runs REPL with all debug flags enabled (PIC_GC_STRESS, VM_DEBUG, DEBUG).
-
-		$ make
-	
 - build
 
-		$ make build
+	A built executable binary will be under bin/ directory and a shared library `libpicrin.so` under lib/.
 	
-	built executable binary will be under bin/ directory and shared library `libpicrin.so` under lib/.
+		$ make
 
 	If you want to build picrin on other systems than x86_64, make sure PIC_NAN_BOXING flag is turned off (see include/config.h for detail).
 
@@ -106,7 +100,11 @@ https://github.com/wasabiz/picrin
 
 		$ make run
 
-In the default option, when `make` command is called without arguments, it builds the binary and right after that dropped into the picrin interactive shell (REPL).
+- debug-run
+
+	When `make` command is called with an argument `debug`, it builds the binary with all debug flags enabled (PIC_GC_STRESS, VM_DEBUG, DEBUG).
+
+		$ make debug
 	
 - install