README file on how to run benchmarks

This gives instruction on the installation and usage and an example of
command line to use.

scripts/benchmark/README.md

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+Script to run an executable (for instance JBMC) on a list of Java methods.
+
+# Install
+
+    npm install
+
+# Usage
+
+    benchmark_java_project.js --help
+
+# Example
+
+Assuming there is a java maven module installed in `project-name/module-core/`,
+and the `jbmc` main directory is in `/path/to/jbmc`, go to
+`project-name/module-core/target/classes`, and run:
+
+    /path/to/scripts/benchmark/benchmark_java_project.js /path/to/jbmc -l method_list_example.txt -a java_arguments.json -m path/to/jbmc/lib/java-models-library/target/core-models.jar | tee result.json
+
+This will display the results and save them into the file `result.json`.
+
+The `method_list_example.txt` file provided here works for `apache-tika/tika-core` available from https://github.com/apache/tika
+
+# Converting the result to csv
+
+    ./benchmark_to_spreadsheet.js result.json >result.csv
+
+This will create a `result.csv` file containing the results.
+
+# Comparing two runs
+
+Assuming the results have been converted to csv and saved into two files named
+benchmark1.csv and benchmark2.csv:
+
+     gnuplot draw_scatter.gp
+
+will create a png file `perf_out.png` with the time from the first run on the
+`y` axis and the second on the `x` axis.