Add external name to the stamping setting example (bazelbuild#1235)

Author: liucijus

docs/scala_import.md

@@ -20,10 +20,13 @@ This rule reimplements `java_import` without support for ijars, which break Scal
 Generally, ijars don’t help much for external dependencies, which rarely change.
 
 The jar's compile MANIFEST.MF is stamped with a Target-Label attribute for dependency tracking 
-reporting. This behaviour can be changed per `scala_import` target with an attribute or globally 
+reporting. 
+
+## Configuring stamping behavior
+This behaviour can be changed per `scala_import` target with an attribute or globally 
 with a setting:
 ```
-bazel build //my:target --//scala/settings:stamp_scala_import=False
+bazel build //my:target --@io_bazel_rules_scala//scala/settings:stamp_scala_import=False
 ```
 
 ## Attributes
@@ -37,4 +40,4 @@ bazel build //my:target --//scala/settings:stamp_scala_import=False
 | exports               | `List of labels, optional` <br> List of targets to add to the dependencies of those that depend on this target.
 | neverlink             | `boolean, optional (default False)` <br> If true only use this library for compilation and not at runtime.
 | srcjar                | `Label, optional` <br> The source jar that was used to create the jar.
-| stamp                 | `Label, optional` <br> Setting to control Target-Label stamping into compile jar Manifest <br> Default value is `@io_bazel_rules_scala//scala/settings:stamp_scala_import`
+| stamp                 | `Label, optional` <br> Setting to control Target-Label stamping into compile jar Manifest <br> Default value is `@io_bazel_rules_scala//scala/settings:stamp_scala_import`