feat: Document offline_support field to manifest.webapp section

Author: Ldoppea

README.md

@@ -243,6 +243,7 @@ Field                            | Description
 `name_prefix`                    | the prefix to display with the name
 `notifications`                  | an object defining how the application can notify the user. See [Notifications](https://docs.cozy.io/en/cozy-stack/apps/#notifications) documentation.
 `oauth`                          | _(konnector specific)_ JSON object containing oAuth information, like `scope`. If a manifest provides an `oauth` property, it is considered as an OAuth konnector. Note: scope can be a string or an array. If it is an array, its values will be joined with a space. A `false` or `null` value in scope will remove any scope parameter in the request sent to the oauth provider.
+`offline_support`                | (Boolean) indicating if the app supports Offline mode when opened from our Flagship applicaiton. See [Flagship Offline mode](https://github.com/cozy/cozy-flagship-app/blob/master/docs/how-to-make-cozy-app-offline-compatible.md) documentation
 `parameters`                     | _(konnector specific)_ Additional parameters which should be passed to the konnector. Used for example for bank konnectors to pass a `bankId` parameter.
 `partnership`                    | an object to provide informations (to display in the Store for example) about a partnership related to the application (`icon` `description`, `name` and `domain`). It can also be used to trigger alternative konnector connection policies for some vendors (see the [budget-insight konnector policy in cozy-harvest](https://github.com/cozy/cozy-libs/blob/065f7e2f3e89efa3b6b49e4ba7f9e20f92825560/packages/cozy-harvest-lib/src/services/budget-insight.js#L123)).
 `permissions`                    | a map of permissions needed by the app (see [see cozy-stack permissions doc ](https://docs.cozy.io/en/cozy-stack/permissions/) for more details)