Add information on tox usage

This patch also adds link to Python Package Index (like for doc8
package) and removes no longer necessary directory change.

Issue-ID: DOC-502
Change-Id: Ibfeda01256babebd3e5224fe766c740bc738e2e8
Signed-off-by: Pawel Wieczorek <p.wieczorek2@samsung.com>
1 file changed