ENH: Updated README with commands to add two new tables

Author: fx86

README.md

@@ -24,6 +24,8 @@ Schema hints are taken from [a post on Meta.StackExchange](http://meta.stackexch
    - `python load_into_pg.py Tags` (not present in earliest dumps)
    - `python load_into_pg.py Users`
    - `python load_into_pg.py Votes`
+   - `python load_into_pg.py PostHistory`
+   - `python load_into_pg.py Comments`
  - Finally, after all the initial tables have been created:
    - `psql stackoverflow < ./sql/final_post.sql`
    - If you used a different database name, make sure to use that instead of