benchmarks: update readme.txt

Remove references to google_speed.proto which was removed in
commit 2e83110230.

Also fix-up commands to build and run.

benchmarks/readme.txt

@@ -22,29 +22,25 @@ Running a benchmark (Java)
    $ javac -d tmp -cp protobuf.jar ProtoBench.java
    
 3) Generate code for the relevant benchmark protocol buffer, e.g.
-   $ protoc --java_out=tmp google_size.proto google_speed.proto
+   $ protoc --java_out=tmp google_size.proto
    
 4) Build the generated code, e.g.
-   $ cd tmp
-   $ javac -d . -cp ../protobuf.jar benchmarks/*.java
+   $ javac -d tmp -cp protobuf.jar tmp/benchmarks/*.java
            
 5) Run the test. Arguments are given in pairs - the first argument
    is the descriptor type; the second is the filename. For example:
-   $ java -cp .;../protobuf.jar com.google.protocolbuffers.ProtoBench
-          benchmarks.GoogleSize$SizeMessage1 ../google_message1.dat
-          benchmarks.GoogleSpeed$SpeedMessage1 ../google_message1.dat
-          benchmarks.GoogleSize$SizeMessage2 ../google_message2.dat
-          benchmarks.GoogleSpeed$SpeedMessage2 ../google_message2.dat
+   $ java -cp tmp:protobuf.jar com.google.protocolbuffers.ProtoBench \
+       'benchmarks.GoogleSize$SizeMessage1' google_message1.dat \
+       'benchmarks.GoogleSize$SizeMessage2' google_message2.dat
           
-6) Wait! Each test runs for around 30 seconds, and there are 6 tests
+6) Wait! Each test runs for around 30 seconds, and there are 8 tests
    per class/data combination. The above command would therefore take
-   about 12 minutes to run.
+   about 8 minutes to run.
 
    
 Benchmarks available
 --------------------
 
 From Google:
-google_size.proto and google_speed.proto, messages
-google_message1.dat and google_message2.dat. The proto files are
-equivalent, but optimized differently.
+google_size.proto,
+messages google_message1.dat and google_message2.dat.