#7 clarify compiler flags

README.md

@@ -38,8 +38,10 @@ Before you start, make sure you have a C++11-compatible compiler (GCC >=
 4.7 is recommended) and the libraries and header files for valgrind,
 zlib, and Berkeley DB.  On Centos, `yum install valgrind-devel zlib-devel
 libdb-devel`, on Ubuntu, `apt-get install valgrind zlib1g-dev libdb-dev`.
-If your default compiler is not new enough, you can pass a different one:
-`scripts/make.mysql.bash --cc=gcc47 --cxx=g++47`.
+
+You can set the compiler by passing `--cc` and `--cxx` to the script, to
+select one that's new enough.  The default is `scripts/make.mysql.bash
+--cc=gcc47 --cxx=g++47`, which may not exist on your system.
 
 
 Contributing