Documentation issue: Type of keys+values of ctx.runfiles's symlinks dict is unclear

Documentation URL: https://docs.bazel.build/versions/2.0.0/skylark/lib/ctx.html#runfiles

> Parameter | Description
> -- | --
> `symlinks` | `dict` The map of symlinks to be added to the runfiles, prefixed by workspace name.

---

The types of the keys and values of this dictionary are unclear. I infer from call sites that it's `dict[string, File]`.

Start at the ctx.runfiles documentation page linked in the issue and read the symlinks parameter entry alongside the call sites mentioned in the report. Clarify the documented types of the dictionary's keys and values; the work is done when the entry explicitly states those types.

Written by the indexing model from the issue text.