how to create table with custom pri key id

using phinx syntax
Update README.md

removed line as requested by @lorenzo
Merge pull request #15 from simkimsia/patch-1

how to create table with custom pri key id
Emphasize learn how to write own migrations 

in phinx syntax
Merge pull request #18 from simkimsia/patch-4

Emphasize learn how to write own migrations