docs: migrate ABOUT-CI and ABOUT-NIGHTLY to dev docs site

Replace relative file links with absolute URLs and add centered page
headers
to the migrated docs. Update the dev sidebar to include the new pages.

1 files changed, 18 insertions, 0 deletions

diff --git a/docs/dev/pages/abouts/nightly-features.md b/docs/dev/pages/abouts/nightly-features.md
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+<h1 align="center">About Nightly Features</h1>
+<p align="center">
+    Using nightly Rust features in Mingling
+</p>
+
+**Mingling** uses some features that are only available in the `nightly` toolchain. This requires you to enable the `nightly` feature:
+
+```toml
+[dependencies]
+mingling = { version = "...", features = ["nightly"] }
+```
+ 
+## Features
+
+> [!WARNING]
+> The following features can only be used with the nightly toolchain, and are only guaranteed to compile, not to be stable or production-ready.
+>
+> If you need a stable development experience, please **do not use** the `nightly` feature!