modified: readme.md

    add instructions for usages

readme.md

@@ -4,6 +4,19 @@ Reproduce MPI message sequences from MPI message logs.
 
 It could be used to testing network performance.
 
+The program contains two parts:
+
+- replayer: the program and tools for recording and playing the
+  mpi logs
+- openmpi: the example patched openmpi using the recording tool
+  to record mpi logs
+
+## USGAE
+
+1. compile the replayer
+
+2. compile the patched openmpi. Add `-I/path/to/replayer/include` and `-L/path/to/replayer/lib -lGlobalComm` to compile options.
+
 ## LOG FORMAT
 
 The log content will be pure numbers, and it could be stored as