[A-docs] Numbers of methods of arg and app building in FAQ.md are wrong.

[vi]

Please complete the following tasks

• I have searched the discussions
• I have searched the existing issues

Rust Version

Not applicable

Clap Version

v3.0.0-rc.4

Minimal reproducible code

Not applicable

Steps to reproduce the bug with the above code

Look at https://github.com/clap-rs/clap/blob/v3.0.0-rc.4/docs/FAQ.md, linked from README:

To build an App there are three [?]:

• Derive Macros
• Builder Pattern

To build an Arg there are four [?]:

• Derive Macros
• Builder Pattern

Actual Behaviour

FAQ.md's app and arg creation lists' introductory phrases are contradictory, probably leftover from Clap v2.

Expected Behaviour

FAQ does not contain phrases that are not play well with actual content in it.

Additional Context

No response

Debug Output

No response