Improve the documentation for running geo benchmark

[jainankitk]

The instructions in the main page documentation mention:

This one is different and self-contained. Read the command-line examples at the top of src/main/perf/IndexAndSearchOpenStreetMaps.java

And on top of src/main/perf/IndexAndSearchOpenStreetMaps.java, we have below:

  // STEPS:                                                                                                                                                                                                                           
  //                                                                                                                                                                                                                                  
  //   * Download all files from http://home.apache.org/~mikemccand/geobench and place in a local directory ... this is "all points inside London, UK"                                                                                
  //     plus "2.5 % of all points around the world" from the ~September 2015 export of OpenStreetMaps corpus, plus two polygon files                                                                                                 
  //                                                                                                                                                                                                                                  
  //   * Uncompress it (lzma -d /path/to/...) (1.9 GB)                                                                                                                                                                                
  //                                                                                                                                                                                                                                  
  //   * cd /path/to/lucene, and go into lucene subdir and run "ant jar"                                                                                                                                                              
  //                                                                                                                                                                                                                                  
  //   * tweak the commands below to match your classpath, then run with options like "-geo3d -poly 100 -reindex"                                                                                                                     
                                                                                                                                                                                                                                      
  // javac -cp build/core/classes/java:build/sandbox/classes/java /l/util/src/main/perf/IndexAndSearchOpenStreetMaps.java /l/util/src/main/perf/RandomQuery.java; java -cp /l/util/src/main:build/core/classes/java:build/sandbox/      classes/java perf.IndexAndSearchOpenStreetMaps                                                                                                                                                                                      
                                                                                                                                                                                                                                      
  // rmuir@beast:~/workspace/util$ javac -cp /home/rmuir/workspace/lucene-solr/lucene/build/core/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/sandbox/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/       spatial/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/spatial3d/classes/java src/main/perf/IndexAndSearchOpenStreetMaps.java src/main/perf/RandomQuery.java                                                           
  // rmuir@beast:~/workspace/util$ java -cp /home/rmuir/workspace/lucene-solr/lucene/build/core/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/sandbox/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/        spatial/classes/java:/home/rmuir/workspace/lucene-solr/lucene/build/spatial3d/classes/java:src/main perf.IndexAndSearchOpenStreetMaps                                                                                               
                                                                                                                                                                                                                                      
  // convert geojson to poly file using src/python/geoJSONToJava.py                                                                                                                                                                   
  //                                                                                                                                                                                                                                  
  // e.g. use -polyFile /l/util/src/python/countries.geojson.out.txt.gz

I tried to download http://home.apache.org/~mikemccand/geobench, but the link seems broken. So, we should look into standardizing this benchmark instructions in a README file, and update broken links and references to lucene-solr?

[prudhvigodithi]

Coming from this comment apache/lucene#15446 (comment), I see the this same issue when I want to run the geo benchmark.