README: Grammar fix regarding gcc atomics

Fix an "i.e." to be "e.g.".

Signed-off-by: mitchelltopaloglu <mitchelltopaloglu@gmail.com>

README

@@ -213,7 +213,7 @@ Compiler Notes
 
 - On platforms other than x86-64, ARM, and PPC, Open MPI requires a
   compiler that either supports C11 atomics or the GCC "__atomic"
-  atomics (i.e., GCC >= v4.7.2).
+  atomics (e.g., GCC >= v4.7.2).
 
 - Mixing compilers from different vendors when building Open MPI
   (e.g., using the C/C++ compiler from one vendor and the Fortran