[docs] improve reference to GN slides

The GN slide deck is pretty comprehensive. While that's valuable, it
can also be intimidating for someone trying just to get started with

To help people just getting started, add text describing which slides
are most likely to be relevant to them.

Change-Id: I3fbe12a1c5fda4d9ac862f219c5f8cdf92f35ce5
diff --git a/docs/run-examples.md b/docs/run-examples.md
index 8009097..c31a457 100644
--- a/docs/run-examples.md
+++ b/docs/run-examples.md
@@ -10,9 +10,9 @@
 Open the [`examples/hello_world/BUILD.gn`](/examples/hello_world/BUILD.gn) file.
 If you aren't familiar with GN, take a look at the
-[introductory presentation](https://docs.google.com/presentation/d/15Zwb53JcncHfEwHpnG_PoIbbzQ3GQi_cpujYwbpcbZo/view#slide=id.g119d702868_0_12)
-or [docs](https://gn.googlesource.com/gn/+/master/docs/). In short, GN is a meta
-build system. Its output files serve as inputs to
+[introductory presentation](https://docs.google.com/presentation/d/15Zwb53JcncHfEwHpnG_PoIbbzQ3GQi_cpujYwbpcbZo/view#slide=id.g119d702868_0_12) (slides 5-16 cover the core concepts, and
+slides 17-21 describe debugging commands) or [docs](https://gn.googlesource.com/gn/+/master/docs/).
+In short, GN is a meta build system. Its output files serve as inputs to
 [Ninja](https://ninja-build.org/), the actual build system.
 In this file, the `hello_world` target is a group containing other dependencies,