docs: Add Helm extension docs (#19095)

Merge after this:
- https://github.com/zed-industries/extensions/pull/746

Release Notes:

- N/A

---------

Co-authored-by: Peter Tripp <peter@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

docs/src/languages/helm.md

@@ -0,0 +1,22 @@
+# Helm
+
+Support for Helm in Zed is provided by the community-maintained [Helm extension](https://github.com/cabrinha/helm.zed).
+
+- Tree-sitter: [tree-sitter-go-template](https://github.com/ngalaiko/tree-sitter-go-template/tree/master)
+- Language Server: [mrjosh/helm-ls](https://github.com/mrjosh/helm-ls)
+
+## Setup
+
+Enable Helm language for Helm files by editing your `.zed/settings.json` and adding:
+
+```json
+  "file_types": {
+    "Helm": [
+      "**/templates/**/*.tpl",
+      "**/templates/**/*.yaml",
+      "**/templates/**/*.yml",
+      "**/helmfile.d/**/*.yaml",
+      "**/helmfile.d/**/*.yml"
+    ]
+  }
+```