README example doesn't specify you must create cstore folder path for create table example

[RexGibson]

The readme example create table statement or trouble shooting paragraph should indicate that the /usr/local/postgres/cstore/customer_reviews.cstore path might need to be created if you want to section off all the cstore files into a folder. I had to either change the path to remove that folder, or create the folder while working through the example.

[pykello]

Added a note right after the CREATE TABLE example.