docs: ✏️ Add i18n documentation (#1679)

* docs: ✏️ Add i18n documentation

---------

Co-authored-by: Zhihe Li <zhihe.li@hashicorp.com>
Co-authored-by: lisbet-alvarez <107949262+lisbet-alvarez@users.noreply.github.com>

documentation/README.md

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+# Boundary Developer conventions
+
+## I18n:
+
+We use [ember-intl](https://ember-intl.github.io/ember-intl/) to manage i18n. All the code related to i18n lives within [the core addon](https://github.com/hashicorp/boundary-ui/tree/main/addons/core).
+
+All the features provided by ember-intl are available to use, on top of that, the Boundary team [provides some custom helpers](https://github.com/hashicorp/boundary-ui/tree/main/addons/core/addon/helpers).
+
+### Dates & Time
+
+Dates and time must be expressed when possible using the [`<time>` HTML element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/time).
+
+The desired date format for the Boundary teams is: `YYYY-MM-DD HH-MM-SS TZ`
+
+### Strings
+
+Plain text strings must be avoided, we use a rule [(`no-bare-strings`)](https://github.com/ember-template-lint/ember-template-lint/blob/master/docs/rule/no-bare-strings.md) within our linter to avoid committing plain text strings.
+
+To learn how to add a translation, [check documentation](https://ember-intl.github.io/ember-intl/docs/quickstart#2-add-your-first-translation).
+
+All our translations files are located [in the translations folder](https://github.com/hashicorp/boundary-ui/tree/main/addons/core/translations) within Core Addon, check the specific [translations Readme](https://github.com/hashicorp/boundary-ui/blob/main/addons/core/translations/README.md) to learn more about it.
+
+To learn more how to use a translation on the templates checkout [the `t` helper documentation](https://ember-intl.github.io/ember-intl/docs/helpers/t).