Refine top-level documentation

Author: jserv

README.md

@@ -33,7 +33,7 @@ usage is the same as the mke2fs command.
 
 For most GNU/Linux distributions, `mkfs.ext4` command should be installed in advance.
 For macOS, use the following command:
-```
+```shell
 $ brew install e2fsprogs
 ```
 
@@ -66,26 +66,26 @@ Enter `root` to access shell.
 
 You can exit the emulator using: \<Ctrl-a x\>. (press Ctrl+A, leave it, afterwards press X)
 
-## Build Linux kernel image and root file system
-
-An automated build script is provided to compile the RISC-V cross-compiler, Busybox, and Linux kernel from source.
-Please note that it only supports the Linux host environment.
-
-```shell
-$ make build-image
-```
-
 ## Usage
 
-```
+```shell
 ./semu -k linux-image [-b dtb-file] [-i initrd-image] [-d disk-image]
 ```
 
 * `linux-image` is the path to the Linux kernel `Image`.
 * `dtb-file` is optional, as it specifies the user-specified device tree blob.
-* `initrd-image` is optional, as it specifies the user-specified init RAM disk image.
+* `initrd-image` is optional, as it specifies the user-specified initial RAM disk image.
 * `disk-image` is optional, as it specifies the path of a disk image in ext4 file system for the virtio-blk device.
 
+## Build Linux kernel image and root file system
+
+An automated build script is provided to compile the RISC-V cross-compiler, Busybox, and Linux kernel from source.
+Please note that it only supports the Linux host environment.
+
+```shell
+$ make build-image
+```
+
 ## License
 
 `semu` is released under the MIT License.