doc: complete docs with manual note

docs/README.md

@@ -1,9 +1,41 @@
 # documentations
 
-local :
+### local :
 
 linter required
 
 ```shell
 $ brew install golangci-lint
 ```
+
+firecracker on archlinux
+
+```shell
+pacman -S firecracker
+```
+
+### build
+
+```shell
+make build
+```
+
+### get rootfs and necessary stuff
+
+```shell
+ARCH="$(uname -m)"
+
+# Download a linux kernel binary
+wget https://s3.amazonaws.com/spec.ccfc.min/firecracker-ci/v1.7/${ARCH}/vmlinux-5.10.204
+
+# Download a rootfs
+wget https://s3.amazonaws.com/spec.ccfc.min/firecracker-ci/v1.7/${ARCH}/ubuntu-22.04.ext4
+
+# Download the ssh key for the rootfs
+wget https://s3.amazonaws.com/spec.ccfc.min/firecracker-ci/v1.7/${ARCH}/ubuntu-22.04.id_rsa
+
+# Set user read permission on the ssh key
+chmod 400 ./ubuntu-22.04.id_rsa
+```
+
+cf [Official firecracker getting started](https://github.com/firecracker-microvm/firecracker/blob/main/docs/getting-started.md#getting-started-with-firecracker)