Update "Bootstrap Debian 10 (buster)" section in README.md

Build phase commands refined from #10

.gitignore

@@ -3,3 +3,5 @@ debian
 cache/*
 !cache/.gitkeep
 nk.bin
+image/sd.img
+image/work

README.md

@@ -83,25 +83,15 @@ Build Linux
 Bootstrap Debian 10 (buster)
 ----------------------------
 
-1. Partition an SD card into two partitions.
-
-    - 1st: FAT32 (vfat), about 100MB
-    - 2st: ext4, fill the remaining area
-
-1. Build and copy the Linux kernel.
-
-    - Run `make ldefconfig lbuild`.
-    - Copy `/linux-brain/arch/arm/boot/zImage` and `/linux-brain/arch/arm/boot/dts/imx28-evk.dtb` into the 1st partition.
+1. Run `make ldefconfig lbuild`.
 
 1. Run APT cache in background (mandatory): `make aptcache`.
 
-1. Run `make debian`.
+1. Run `make brainux`.
 
-1. Copy all contents in `./debian` into the 2nd partition.
-
-    - `sudo cp -ar ./debian/* /path/to/your/sd/2nd/partition/`
-    - Please make sure that all attributes are preserved with `-a` flag.
+1. Run `make image.sd.img`
 
+1. Confirm that `image/sd.img` exists.
 
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