Add contributors in README

Author: mrdrivingduck

README.md

@@ -12,13 +12,13 @@ Created by : zSnow && Mr Dk.
 
 By default, the value of `KDIR` in `Makefile` points to the source code directory of **currently running kernel**, on which the kernel module will be installed.
 
-```
+```makefile
 KDIR := /lib/modules/$(shell uname -r)/build
 ```
 
 Also, you can build the module for one kernel on another kernel by overriding the `KDIR` variable. Suppose your directory is a submodule of [linux-kernel-elf-sig-verify](https://github.com/NUAA-WatchDog/linux-kernel-elf-sig-verify) under its directory like `linux-kernel-elf-sig-verify/linux-kernel-elf-sig-verify-module`, then you can modify `KDIR` to:
 
-```
+```makefile
 KDIR := ../
 ```
 
@@ -70,6 +70,8 @@ If the module is installed successfully, you cannot run an ELF file without sign
 
 ## Key for Verification
 
+### Generate Keys By Yourself
+
 The `certs/kernel_key.pem` is the same as the key in [linux-elf-binary-signer](https://github.com/NUAA-WatchDog/linux-elf-binary-signer), and is only used for testing. To use the `binfmt_elf_signature_verification` module, you should compile the key into the kernel.
 
 Or you can use the configuration file to get your own key pair by modifying `certs/x509.genkey`:
@@ -109,8 +111,20 @@ writing new private key to 'kernel_key.pem'
 $ cd ..
 ```
 
+### Generate Keys Through *Let's Encrypt*
+
+See the website of [*Let's Encrypt*](https://letsencrypt.org/) and use [*Certbot*](https://certbot.eff.org/) to generate private key and public key certificate.
+
 ---
 
+## Contributors
+
+<a href="https://github.com/NUAA-WatchDog/linux-kernel-elf-sig-verify-module/graphs/contributors">
+  <img src="https://contributors-img.web.app/image?repo=NUAA-WatchDog/linux-kernel-elf-sig-verify-module" />
+</a>
+
+Made with [contributors-img](https://contributors-img.web.app).
+
 ## License
 
 Copyright © 2020, Jingtang Zhang, Hua Zong. ([MIT License](LICENSE))