docs: update instructions for building win32 target (electron#14560)

nornagon · MarshallOfSound · commit b35c8e4e1e95 · 2018-09-12T12:05:51.000+10:00
diff --git a/docs/development/build-instructions-windows.md b/docs/development/build-instructions-windows.md
@@ -31,11 +31,13 @@ See [Build Instructions: GN](build-instructions-gn.md)
 
 ## 32bit Build
 
-To build for the 32bit target, you need to pass `--target_arch=ia32` when
-running the bootstrap script:
+To build for the 32bit target, you need to pass `target_cpu = "x86"` as a GN
+arg. You can build the 32bit target alongside the 64bit target by using a
+different output directory for GN, e.g. `out/Release-x86`, with different
+arguments.
 
 ```powershell
-$ python script\bootstrap.py -v --target_arch=ia32
+$ gn gen out/Release-x86 --args="import(\"//electron/build/args/release.gn\") target_cpu=\"x86\""
 ```
 
 The other building steps are exactly the same.
