add readme help text for benchmark

python/tools/README.md

+# Benchmark
+
+The `benchmark.py` script is used for testing OpenDHT in various cases. If you
+run `benchmark.py --help`, you should find the following text:
+
+    optional arguments:
+      -h, --help            show this help message and exit
+      --performance         Launches performance benchmark test. Available args
+                            for "-t" are: gets.
+      --data-persistence    Launches data persistence benchmark test. Available
+                            args for "-t" are: delete, replace, mult_time.
+                            Available args for "-o" are : dump_str_log,
+                            keep_alive, trigger, traffic_plot, op_plot. Use "-m"
+                            to specify the number of producers on the DHT.Use "-e"
+                            to specify the number of values to put on the DHT.
+
+These options specify the feature to be tested. Each feature has its own tests.
+You specify the test by using `-t` flag (see `benchmark.py --help` for full
+help).
+
+## Python dependencies
+
+- pyroute2 >=0.3.14
+- matplotlib
+- GeoIP (used by `scanner.py` for drawing map of the world)
+- ipaddress
+- netifaces
+- networkx
+- numpy
+
+## Usage
+
+Before running the script, you have to build and install OpenDHT and its cython
+wrapper (`cython3` has to be installed) on the system so that it can be found by
+the benchmark script.
+
+    $ cd $OPENDHT_SRC_DIR
+    $ ./autogen.sh
+    $ ./configure
+    $ make && sudo make install
+
+Then, you can use the script like so:
+
+    $ cd $OPENDHT_SRC_DIR/python/tools/
+    $ python3 benchmark.py --performance -t gets -n 2048