docs: add fuzz pointer, AI policy, playground link, and Ubuntu note

Author: sylvestre

CONTRIBUTING.md

@@ -38,6 +38,7 @@ parts for getting started:
 - [`docs`](https://github.com/uutils/coreutils/tree/main/docs/src): the documentation for the website
 - [`tests/uutests/`](https://github.com/uutils/coreutils/tree/main/tests/uutests/):
   Crate implementing the various functions to test uutils commands.
+- [`fuzz/`](https://github.com/uutils/coreutils/tree/main/fuzz/): The differential fuzzers.
 
 Each utility is defined as a separate crate. The structure of each of these
 crates is as follows:
@@ -68,7 +69,8 @@ We have the following goals with our development:
 - **Performant**: Our utilities should be written in fast idiomatic Rust. We aim
   to match or exceed the performance of the GNU utilities.
 - **Well-tested**: We should have a lot of tests to be able to guarantee
-  reliability and compatibility.
+  reliability and compatibility. Code coverage should not regress; new
+  behavior should come with tests that cover it.
 
 ## How to Help
 
@@ -194,6 +196,16 @@ If you edit a piece of code, make sure to update any comments that need to
 change as a result. The only thing worse than having no comments is having
 outdated comments!
 
+## AI policy
+
+AI-assisted contributions are allowed, but the same standards apply as for
+any other patch. If you use an AI tool to help write a change, you are still
+responsible for it: you should understand every line you submit and be able
+to explain and justify the change in review. Keep patches small and focused
+so they are easy to review, and self-review the diff carefully before opening
+a pull request - reviewers are there to double-check a human's work, not an
+LLM's output.
+
 ## Git Etiquette
 
 To ensure easy collaboration, we have guidelines for using Git and GitHub.

README.md

@@ -52,6 +52,8 @@ uutils aims to work on as many platforms as possible, to be able to use the same
 utils on Linux, macOS, Windows and other platforms. This ensures, for example,
 that scripts can be easily transferred between platforms.
 
+uutils coreutils ships by default on Ubuntu since version 25.10.
+
 <div class="oranda-hide">
 
 ## Documentation
@@ -65,6 +67,10 @@ the [coreutils docs](https://github.com/uutils/uutils.github.io) repository.
 
 Use [weblate/rust-coreutils](https://hosted.weblate.org/projects/rust-coreutils/) to translate the Rust coreutils into your language.
 
+You can try the utilities in your browser through the
+[WebAssembly playground](https://uutils.github.io/playground/), without
+installing anything.
+
 <!-- ANCHOR: build (this mark is needed for mdbook) -->
 
 ## Requirements