docs: extension bundling (#2068)

developers.md

@@ -9,6 +9,7 @@
   - [Oneshot job](#oneshot-job)
   - [Previewer](#previewer)
   - [More examples](#more-examples)
+  - [Bundling as Extension](#bundling-as-extension)
 - [Technical](#technical)
   - [picker](#picker)
   - [finders](#finders)
@@ -278,6 +279,51 @@ more information on [gitter](https://gitter.im/nvim-telescope/community?utm_sour
 and we will happily answer your questions and hopefully allow us to improve this guide. You can also
 help us to improve this guide by sending a PR.
 
+### Bundling as extension
+
+If you now want to bundle your picker as extension, so it is available as
+picker via the `:Telescope` command, the following has to be done.
+
+Structure your plugin as follows, so it can be found by telescope:
+
+```
+.
+└── lua
+    ├── plugin_name             # Your actual plugin code
+    │   ├── init.lua
+    │   └── some_file.lua
+    └── telescope
+        └── _extensions         # The underscore is significant
+            └─ plugin_name.lua  # Init and register your extension
+```
+
+The `lua/telescope/_extensions/plugin_name.lua` file needs to return the
+following: (see `:help telescope.register_extension`)
+
+```lua
+return require("telescope").register_extension {
+  setup = function(ext_config, config)
+    -- access extension config and user config
+  end,
+  exports = {
+    stuff = require("plugin_name").stuff
+  },
+}
+```
+
+The setup function can be used to access the extension config and setup
+extension specific global configuration. You also have access to the user
+telescope default config, so you can override specific internal function. For
+example sorters if you have an extension that provides a replacement sorter,
+like
+[telescope-fzf-native](https://github.com/nvim-telescope/telescope-fzf-native.nvim).
+
+The exports table declares the exported pickers that can then be accessed via
+`Telescope plugin_name stuff`. If you only provide one export it is suggested
+that you name the key like the plugin, so you can access it with `Telescope
+plugin_name`.
+
+
 ## Technical
 
 ### Picker