adding all-contributors table for core team members

[jlooper]

Summary

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

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

If changing the UI of default theme, please provide the before/after screenshot:

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

• Yes
• [x ] No

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

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• [ x] Chrome
• Firefox
• Safari
• Edge
• IE

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

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

This PR adds a grid for Core Team members to add themselves and their capacities as Core members. Other members can add themselves to .all-contributorsrc and then regenerate the grid on the README.md file via yarn all-contributors generate

[ulivz]

Just merged this pull request, if there are new members, feel free to submit PR ~

[vue-bot]

Hey @jlooper, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚