Allow set `base` from CLI options when build

[haoranpb]

Feature request

I came across the relative question on StackOverflow, and found a solution in #560 ,but I think this feature would allow people to solve the problem more easily.

What problem does this feature solve?

Give user more flexibility while setting base.

What does the proposed API look like?

yarn docs:build --base <base>

How should this be implemented in your opinion?

Are you willing to work on this yourself?

Gladly