[dpdk-web] update of "Contribute" page

[Thomas Monjalon]

Hi,

I would like to propose an update of this page:
	https://www.dpdk.org/contribute/
It is supposed to be a welcome page for contributors of any DPDK project,
not only the core one. So we can remove some redundancy with the page
about contributing to DPDK Core.
One more change: we have a new code.dpdk.org service to advertise.

We can keep this introduction:
"
DPDK is an open source project, with the main code BSD licensed and Linux kernel related parts are naturally licensed under the GPL. We welcome and encourage anyone who is interested to contribute and participate in the project.
"
The second part of the introduction requires some changes:
"
The collaboration is based on git and emails. Coming patches are listed in patchwork. Bugs are open in bugzilla. The Technical Board may intermediate in the development process, as described in the Technical Board operation.
"
The link on "git" must be changed to http://git.dpdk.org so that it covers all repositories.
The link on "emails" must be to the following section listing all mailing-lists.
The link on "patchwork" must cover any possible new project: https://patches.dpdk.org
The sentence about the roadmap is removed because specific to Core.
The link on "bugzilla" must cover all projects: https://bugs.dpdk.org

We should add a sentence to link to the "Contribute" page of the Core project:
"
The main project has specific informations for contributors.
Other projects have their own documentation.
"
with "informations for contributors" being a link to https://core.dpdk.org/contribute
and "documentation" being a link to https://www.dpdk.org/hosted-projects/

The next section "Get the Code" can be replaced by a list of links to services
available to the contributors:
	- Code - code.dpdk.org
	- Repositories - git.dpdk.org
	- Patches - patches.dpdk.org
	- Email archives - inbox.dpdk.org
	- Bugs - bugs.dpdk.org

The section "Mailing Lists" should stay as is.

The section "Ways to Contribute" is an old copy of the Core project,
so it should be completely removed from this general page.

Any comment?