Add missing I18n section.

One section is completely mission so far - an important one: I18n
I18n (Internationalization) and L10n (Localization) are also quite important topics around international websites.

Adds proposal for

* https://github.com/auraphp/Aura.Intl

along with it.
This will render badly.

    * Libraries for I18n (Internationalization) and L10n (Localization)*

will be render as:

* Libraries for I18n (Internationalization) and L10n (Localization)*

And

    *Libraries for I18n (Internationalization) and L10n (Localization)*

will be rendered as:

*Libraries for I18n (Internationalization) and L10n (Localization)*