docs: Add a short sections on helpers (#1093)

docs/helpers.md

@@ -0,0 +1,39 @@
+# Helpers
+
+Regardless of the way NixVim is used (as a home-manager module, a nixos module, or as a standalone module),
+helpers can be included in the same way.
+
+You can simply use:
+
+```nix
+{
+    helpers,
+    ...
+}: {
+    # Your config
+}
+```
+
+A certain number of helpers are defined that can be useful:
+
+- `helpers.emptyTable`: An empty lua table `{}` that will be included in the final lua configuration.
+  This is equivalent to `{__empty = {};}`. This form can allow to do `option.__empty = {}`.
+
+- `helpers.mkRaw str`: Write the string `str` as raw lua in the final lua configuration.
+  This is equivalent to `{__raw = "lua code";}`. This form can allow to do `option.__raw = "lua code"`.
+
+- `helpers.toLuaObject obj`: Create a string representation of the Nix object. Useful to define your own plugins.
+
+- `helpers.listToUnkeyedAttrs list`: Transforms a list to an "unkeyed" attribute set.
+
+  This allows to define mixed table/list in lua:
+
+  ```nix
+    (listToUnkeyedAttrs ["a", "b"]) // {foo = "bar";}
+  ```
+
+  Resulting in the following lua:
+
+  ```lua
+    {"a", "b", [foo] = "bar"}
+  ```