Update commands in docs

[viktordanko]

Hey, I came across to this during installation, so just FYI :]

Current:

# Yarn:
yarn add --dev @strv/stylelint-config

# npm:
npm install --save-dev @strv/stylelint-config

Expected:

# Yarn:
yarn add --dev @strv/stylelint-config-styled-components

# npm:
npm install --save-dev @strv/stylelint-config-styled-components

[dannytce]

Thank you @viktordanko for noticing! :) Will update together with next release