All the links in https://sqlflow.org/sqlflow/doc/quick_start/ leads to 404

**Description**
All the links in https://sqlflow.org/sqlflow/doc/quick_start/ leads to 404.
**Reproduction Steps**
Click any of the links on the bottom of the page.

**Expected Behavior**
The links lead to proper pages.

**Screenshots**

**Environment (Please complete the following information):**
 - OS:
 - Browser:
 - Version:

**Additional Notes**