Update doc

Documentation/docs/plugins.md

@@ -86,6 +86,12 @@
 - `plugins.external_prefix` (only if installed outside of the docker) is the external prefix of the plugin. When the frontend will call https://tdrive.app/plugins/onlyoffice/ it will be redirected to the internal_domain.
 - **If your server and frontend runs on different urls** then you must replace all the /plugins[...] by http://my_server_url/plugins[...] except for the external_prefix URI.
 
+#### You can also set it using env variables
+
+```
+APPLICATIONS='{ "grid": [ { "name": "Tmail", "logo": "/public/img/grid/tmail.png", "url": "https://tmail.linagora.com/" } ], "plugins": [ { "id": "tdrive_onlyoffice", "internal_domain": "http://plugins_onlyoffice:5000/", "external_prefix": "/plugins/onlyoffice/", "api": { "private_key": "apisecret" }, "display": { "tdrive": { "version": 1, "files": { "editor": { "preview_url": "/plugins/onlyoffice/?preview=1", "edition_url": "/plugins/onlyoffice/", "empty_files": [ { "url": "/plugins/onlyoffice/assets/empty.docx", "filename": "Untitled.docx", "name": "ONLYOFFICE Word Document" }, { "url": "/plugins/onlyoffice/assets/empty.xlsx", "filename": "Untitled.xlsx", "name": "ONLYOFFICE Excel Document" }, { "url": "/plugins/onlyoffice/assets/empty.pptx", "filename": "Untitled.pptx", "name": "ONLYOFFICE PowerPoint Document" } ], "extensions": [ "xlsx", "pptx", "docx", "xls", "ppt", "doc", "odt", "ods", "odp", "txt", "html", "csv" ] } } } }, "identity": { "code": "only_office", "name": "Only Office", "icon": "/plugins/onlyoffice/assets/logo.png", "description": null, "website": "http://twake.app/", "categories": [], "compatibility": ["tdrive"] } } ] }'
+```
+
 ## Add and run the docker container for the plugin
 
 For instance with onlyoffice, you can find the plugin here: https://github.com/linagora/Twake-Plugin-Onlyoffice