docs: Explain parallel build
Thanks to Michal Altmann for reminding me about this.
Change-Id: I4fdbb7bfc501fc8010723b4abaf889c7f25317d8
diff --git a/README.md b/README.md
index 7aa5672..d3be306 100644
--- a/README.md
+++ b/README.md
@@ -32,8 +32,11 @@
WARNING: Buildroot is fragile.
It is *not* safe to perform incremental builds after changing an "important" setting.
Please check their manual for details.
-Using `ccache` might help, but a significant time is wasted in `configure` steps which are not parallelized :( as of October 2017.
-This can be hacked by patching Buildroot's top-level `Makefile`, but note that one cannot easily debug stuff afterwards:
+
+### Hack: parallel build
+
+A significant amount of time is wasted in `configure` steps which are not parallelized :( as of November 2017.
+This can be hacked by patching Buildroot's top-level `Makefile`, but note that one cannot easily debug stuff afterwards.
```diff
diff --git a/Makefile b/Makefile
@@ -50,6 +53,12 @@
TOPDIR := $(CURDIR)
```
+Also, we are building two different root filesystem instances (an EXT4 image and a tarball for RAUC).
+This is [also currently broken](http://lists.busybox.net/pipermail/buildroot/2017-November/206255.html), but we can work around that reasonably easily:
+
+```sh
+make -j32 target-finalize && make
+```
## Installing updates to a device