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

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 +196,19 @@ 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 outdated comments!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. Be especially careful that the
+output is not derived from GNU coreutils or other GPL code - AI assistants
+are trained on GPL sources and can reproduce them verbatim, which this
+project cannot accept. 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

@@ -54,6 +54,8 @@ uutils aims to work on as many platforms as possible, to be able to use the same
 utils on Linux, macOS, *BSD, Windows, WASI 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
@@ -67,6 +69,10 @@ 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