refactor tikv.org

[zz-jason]

Change Request

Describe the problem

The current content of https://tikv.org/ is too simple, the current introduction for TiKV is:

A distributed transactional key-value database

Based on the design of Google Spanner and HBase, but simpler to manage and without dependencies on any distributed filesystem

There aren't any use cases and TiKV adoptors displayed on the page. In one word, As a user, I don't know whether TiKV can solve my problem to grow my business.

Suggest an improvement/fix

Refactor the current homepage for https://tikv.org/ to display:

• what's TiKV, focused on the value proposition for users
• why choosing TiKV, what makes it outstanding compared with the similar solutions
• who are using TiKV
• use cases, help me to find the similar scenarios
• how to get started with TiKV

[zz-jason]

@marsishandsome @andylokandy PTAL