docs(README): New swicth: 400 stations only

This allows us to have a way to compare with the original Java challenge

Author: gcarreno

README.md

@@ -109,6 +109,7 @@ In order to produce the One Billion Rows of text, we are providing the [source c
 | **-i** or **--input-file \<filename\>** | The file containing the Weather Stations |
 | **-o** or **--output-file \<filename\>** | The file that will contain the generated lines |
 | **-n** or **--line-count \<number\>** | The amount of lines to be generated ( Can use 1_000_000_000 ) |
+| **-4** or **--400stations** | Only 400 weather stations in output file |
 
 ## Baseline
 > **NOTE**