add initial demo pthread party

Everything in order here. Party results:

Before party:
FOOD:  [ *********** ]
TRASH: [             ]

After party:
FOOD:  [             ]
TRASH: [ *********** ]

Everyone ate in order and then placed their trash accordingly.
Locking is in place so this is expected.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>