README update to include Vue Land as questions resource and chat badges

[jdaltonchilders]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
This PR is an update to the README file to include the Vue Land chat hosted by Discord. 😄 Although @egoist has mentioned the chat on Twitter I thought it'd be a good idea to include it in the README so new and old Vue developers know about the resource. Also, I added badges for both the Discord and Gitter chats.

Since this PR made no changes to Vue's codebase I neglected to run any test.

[posva]

Thanks for the PR. We'll look at this after the Vue conf (vuejs/v2.vuejs.org#959)