[TOOLS] Add new tools (PKUFlyingPig#577)

* Update tools.md

add free Synergy which A set of keyboard and mouse controls for multiple computers

* Update tools.en.md

add a set of keyboard and mouse controls for multiple computers

Author: askxiaozhang

docs/必学工具/tools.en.md

@@ -100,3 +100,4 @@
 - [keybr](https://www.keybr.com/): A website for learning touch typing.
 - [Awesome C++](https://cpp.libhunt.com/): A curated list of awesome C/C++ frameworks, libraries, resources.
 - [HelloGitHub](https://hellogithub.com/): Shares interesting and beginner-friendly open-source projects on GitHub.
+- [Synergy](https://github.com/DEAKSoftware/Synergy-Binaries): A set of keyboard and mouse controls for multiple computers

docs/必学工具/tools.md

@@ -98,3 +98,4 @@
 - [keybr](https://www.keybr.com/): 学习盲打的网站。
 - [Awesome C++](https://cpp.libhunt.com/): 很棒的 C/C++ 框架、库、资源精选列表。
 - [HelloGitHub](https://hellogithub.com/): 分享 GitHub 上有趣、入门级的开源项目。
+- [Synergy](https://github.com/DEAKSoftware/Synergy-Binaries): 一套键鼠能控制多台电脑。