Fix example in README

[davidtheclark]

Just added () when bemLinter is invoked, because otherwise the plugin won't actually run.

Intest.js, that's how it is invoked: postcss().use(linter()).process(css);.

Alternately, index.js could be modified to return a function with the parameters (css, opts), as explained here: https://github.com/postcss/postcss#processor --- then linter could be invoked without the (), I believe.

[davidtheclark]

This comment from @ai applies: postcss/postcss#149 (comment)

[MoOx]

Also:

• Convention use(plugin()) should be maintained ianstormtaylor/rework-color-function#6
• https://twitter.com/jongleberry/status/496552790416576513

[ai]

We had a onversation here: postcss/postcss#149

Let’s wait for issues in plugins until we finish plugin guidelines.

[ai]

But I really think that we should allow to miss () without a options. In all examples you do not use require('plugin-name') and it is a mistake. Most of PostCSS user cases will looks like:

postcss([ require('plugin1'), require('plugin2') ]);

Nobody will save 10-15 plugins to variables to use them only once.

And in this cases require('plugin')() looks weird.

[ai]

But the main reason is that require('plugin')() is unsafe. If you will forgot about () (and new users always don’t read docs carefully) your plugin will not work without any warning.

[necolas]

Fixed by #13