Fix README about getting started

[gold-kou]

Thank you for an awesome starting tool to develop an API server ✨

I was a bit confused about getting started in README.
Because I think Installation should be ahead before getting started.

And I found I have to cd <application> to generate service.
Correct?

Thank you.

[codecov-commenter]

Codecov Report

Merging #263 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #263   +/-   ##
=======================================
  Coverage   60.09%   60.09%           
=======================================
  Files          32       32           
  Lines        1218     1218           
=======================================
  Hits          732      732           
  Misses        436      436           
  Partials       50       50           

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