Update URL for global HACKING document

* Related to I579e7c889f3addc2cd40bce0c584bbc70bf435e2
* Rename local-checks section to make it clearer

Change-Id: If4e006368c09dcd6c87ebf7a2aba448c9a9390de
Add -U flag to pip install command

The -U flag makes tox able to upgrade all packages to the newest available
version.

Change-Id: Ibe5fa0115c2b151ae6f3bd741cc561d2435499e8
Merge "Add -U flag to pip install command"