Document how to remove plugins

[benjie]

Also expose this via the CLI and via .postgraphilerc

[benjie]

Ref: graphile/crystal#714

[eladkolet]

Hey @benjie , is they a way to remove both of the default generation of "itemById(id: Int!)" and "itemByUniqueKey1AndUniqueKey2(uniqueKey1: ...)" and also disable the NodePlugin ?

Thanks!

[benjie]

Something like this:

app.use(postgraphile(process.env.DATABASE_URL, ['app_public'], {
  skipPlugins: [
    require('graphile-build').NodePlugin,
    require('graphile-build-pg').PgRowByUniqueConstraint,
  ],
}));