docs(ref): Have workspace docs link out to resolver field docs

This is a part of the schema we were missing.  A first step before
encouraging people to use it is to document it!

Author: epage

src/doc/src/reference/workspaces.md

@@ -29,6 +29,7 @@ See also [`default-members`](#the-default-members-field)
 The `[workspace]` table supports the following sections:
 
 * [`[workspace]`](#the-workspace-section) — Defines a workspace.
+  * [`resolver`](resolver.md#resolver-versions) — Sets the dependency resolver to use.
   * [`members`](#the-members-and-exclude-fields) — Packages to include in the workspace.
   * [`exclude`](#the-members-and-exclude-fields) — Packages to exclude from the workspace.
   * [`default-members`](#the-default-members-field) — Packages to operate on when a specific package wasn't selected.