runtime/metrics: godoc link fixes

Fix rendering of link to runtime/debug.ReadGCStats in package overview:
as the package is not imported we must specify the absolute package
name.

Change-Id: I123db49eee05e6812427e19873e628b4e4feb203
Reviewed-on: https://go-review.googlesource.com/c/go/+/549735
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Run-TryBot: qiulaidongfeng <[email protected]>
Reviewed-by: qiulaidongfeng <[email protected]>

Author: dolmen

src/runtime/metrics/doc.go

@@ -8,7 +8,7 @@
 /*
 Package metrics provides a stable interface to access implementation-defined
 metrics exported by the Go runtime. This package is similar to existing functions
-like [runtime.ReadMemStats] and [debug.ReadGCStats], but significantly more general.
+like [runtime.ReadMemStats] and [runtime/debug.ReadGCStats], but significantly more general.
 
 The set of metrics defined by this package may evolve as the runtime itself
 evolves, and also enables variation across Go implementations, whose relevant
@@ -28,7 +28,8 @@ encouraged to use build tags, and although metrics may be deprecated and removed
 users should consider this to be an exceptional and rare event, coinciding with a
 very large change in a particular Go implementation.
 
-Each metric key also has a "kind" that describes the format of the metric's value.
+Each metric key also has a "kind" (see [ValueKind]) that describes the format of the
+metric's value.
 In the interest of not breaking users of this package, the "kind" for a given metric
 is guaranteed not to change. If it must change, then a new metric will be introduced
 with a new key and a new "kind."