Some documentation for the jumbo feature.

docs/windows_build_instructions.md

Index: docs/windows_build_instructions.md
diff --git a/docs/windows_build_instructions.md b/docs/windows_build_instructions.md
index c4c282c6d89c2a6c62c6ef90fa8210c208b2decc..1c3406e169a1c894544d254c6990587edc02c1ee 100644
--- a/docs/windows_build_instructions.md
+++ b/docs/windows_build_instructions.md
@@ -199,6 +199,7 @@ in the editor that appears when you create your output directory
 (`gn args out/Default`) or on the gn gen command line
 (`gn gen out/Default --args="is_component_build = true is_debug = true"`).
 Some helpful settings to consider using include:
+* `use_jumbo_builds = true` - *Experimental* [Jumbo/unity](jumbo.md) builds.
 * `is_component_build = true` - this uses more, smaller DLLs, and incremental
 linking.
 * `use_nacl = false` - this disables Native Client which is usually not needed for