docs(chart): add note about `.helmignore` for `.Files`

docs/charts.md

@@ -589,9 +589,10 @@ sensitive_.
   `Chart.Maintainers`.
 - `Files`: A map-like object containing all non-special files in the chart. This
   will not give you access to templates, but will give you access to additional
-  files that are present. Files can be accessed using `{{index .Files "file.name"}}`
-  or using the `{{.Files.Get name}}` or `{{.Files.GetString name}}` functions. You can
-  also access the contents of the file as `[]byte` using `{{.Files.GetBytes}}`
+  files that are present (unless they are excluded using `.helmignore`). Files can be
+  accessed using `{{index .Files "file.name"}}` or using the `{{.Files.Get name}}` or
+  `{{.Files.GetString name}}` functions. You can also access the contents of the file
+  as `[]byte` using `{{.Files.GetBytes}}`
 - `Capabilities`: A map-like object that contains information about the versions
   of Kubernetes (`{{.Capabilities.KubeVersion}}`, Tiller
   (`{{.Capabilities.TillerVersion}}`, and the supported Kubernetes API versions