add installation instructions to pkg packages

BUG=

Review URL: https://codereview.chromium.org//14188048

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/stack_trace@21770 260f80e4-7a28-3924-810f-c04153c831b5
1 file changed
tree: d9ad16b060f7d01fbfd47b058c3adfe771104a1e
  1. pkgs/