docs: fix and refresh CONTRIBUTING.md

- Correct the wrong email domain (changkun dot us -> changkun dot de)
- Fix a copy-paste link that pointed at the go-under-the-hood repo
- Update stale C++11/14/17(/20) branding to C++11 to C++26
- Replace the discouraging 'must fix >50 typos' rule with a welcoming
  'fixes of any size are welcome; batch trivial typos' guideline

Author: changkun

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 ## Submit Issue
 
-C++ 11/14/17 issue is used to track the principle description error, `typo` error, and the questions to the author of the book.
+The issue tracker for this book (covering C++11 to C++26) is used to track principle description errors, `typo` errors, and questions to the author of the book.
 
 - Usually, you may encounter typos, semantic errors, grammatical errors, and etc. These are all `typo` errors. If an error has caused some obstacles to your reading and you strongly believe that the `typo` will also affect others reading, then you are very welcome to [submit issue](https://github.com/changkun/modern-cpp-tutorial/issues) to report the `typo` error.
 
@@ -15,15 +15,15 @@ Report the error immediately by [submitting issue](https://github.com/changkun/m
 
 ## Pull Request
 
-"C++ 11/14/17 On the Fly" is open source so that everyone can contribute to contribute via a PR. However, it is required to read the following instructions carefully before submitting your pull request:
+"Modern C++ Tutorial: C++11 to C++26 On the Fly" is open source so that everyone can contribute via a PR. Please read the following instructions carefully before submitting your pull request:
 
 - Before you submit your pull request, make sure that the [issue list](https://github.com/changkun/modern-cpp-tutorial/issues) already contains the problem you want to solve. If not, please refer to the **Submit Issue** section.
 
-- Make sure your PR has improved more than 50 `typo` errors, otherwise please do not submit a PR.
+- Fixes of any size are welcome. For trivial `typo` fixes, please consider batching several of them into a single PR rather than opening many tiny PRs.
 
 - For a PR that fixes principled errors, please don't hesitate, all of the readers of the book are very grateful for your contribution!
 
-- If you would like to be a co-author of this book, please send an email to ask: `hi at changkun dot us`.
+- If you would like to be a co-author of this book, please send an email to ask: `hi at changkun dot de`.
 
 Since this repository provides a variety of reading approaches, thus make sure you have checked all items in the following checklist:
 
@@ -35,7 +35,7 @@ Since this repository provides a variety of reading approaches, thus make sure y
 
 ## 提交 Issue
 
-『C++ 11/14/17/20』的 issue 用于追踪书中存在的原则性的描述错误、存在的 `typo` 错误，以及向本书作者提问等。
+本书（覆盖 C++11 到 C++26）的 issue 用于追踪书中存在的原则性的描述错误、存在的 `typo` 错误，以及向本书作者提问等。
 
 - 通常情况下，你可能会发现书中某个段落存在错别字、语义错误、文法错误等。
 这都是 `typo` 错误。如果该错误已经对你的阅读造成了一定障碍，
@@ -51,18 +51,18 @@ Since this repository provides a variety of reading approaches, thus make sure y
 - 如果你在阅读本书的时候发现有部分内容难于理解，也欢迎[提交 issue](https://github.com/changkun/modern-cpp-tutorial/issues) 来询问作者表达你的疑惑。
 作者会根据实际情况重新优化这一部分的内容，进而帮助他人更易阅读这部分的内容。
 
-- 我们也欢迎你提交针对本书内容的相关建议，具体来说如果你认为书中未涉及的某个模块或者文件的源码值得讨论，也欢迎 [提交 issue](https://github.com/changkun/go-under-the-hood/issues) 来进一步讨论。
+- 我们也欢迎你提交针对本书内容的相关建议，具体来说如果你认为书中未涉及的某个模块或者文件的源码值得讨论，也欢迎 [提交 issue](https://github.com/changkun/modern-cpp-tutorial/issues) 来进一步讨论。
 
 ## 提交 Pull request
 
-『C++ 11/14/17/20』是一本开源书籍，任何人都可以参与贡献自己 PR。但在提交 PR 之前请仔细阅读下面的说明：
+『现代 C++ 教程：高速上手 C++11 到 C++26』是一本开源书籍，任何人都可以参与贡献自己 PR。但在提交 PR 之前请仔细阅读下面的说明：
 
 - 当你认为需要提交一个 PR 时，请确保 [issue 列表](https://github.com/changkun/modern-cpp-tutorial/issues)中，已经包含了你想要解决的问题。
 如果没有，请参考**提交 Issue** 一节中的描述，提交你的 issue，再提交你的 PR。
 
-- 当你准备提交一个 typo 错误的 PR 时，请确保你的 PR 改进了 **超过 50 个汉字(或英文单词)** 的 `typo` 错误，否则请不要提交 PR。
+- 任何大小的修正都欢迎。对于细小的 `typo` 修正，建议将多处一并合入到同一个 PR 中，而不是分散为许多零碎的 PR。
 - 对于一个修复原则性错误的 PR，请不要犹豫，笔者对此表示非常感谢！
-- 如果非常喜欢本书，以至于希望参与本书的合著，成为作者，请发邮件询问：`hi at changkun dot us`。
+- 如果非常喜欢本书，以至于希望参与本书的合著，成为作者，请发邮件询问：`hi at changkun dot de`。
 
 本仓库提供了多种阅读方式，如果你提交一个 Pull request，则请确保你检查的如下的 checklist：