Add "Click to tweet" button on project pages.

[juliaelman]

Description
We'd like to make it super easy for users to share the projects they're helping on via social media. The first step of this was #329.

Ask
Please add a one-click way to share information about a project from the platform on twitter (or other networks if it's easy). Essentially, a click to tweet button from the project page (or even the partial on the projects index list).

To Do

• Embed a click-to-tweet button with template on each Project page that makes it easy to share a quick description of the project.

Additional Info
Where to Share From:

• On Individual Project page
• On Projects index page

Content Ideas:

• include the organization's handle, if available
• include via @CodeMontage
• include short description of project
• Include cause and/or technology hashtags