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

[sylvestre]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/symlink (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.
Note: The gnu test tests/tail/pipe-f is now being skipped but was previously passing.

[collinfunk]

I find the AI policy quite unfortunate given the unclear copyright implications. One can see questionable citations already:

• coreutils/src/uu/mv/src/mv.rs

  Lines 933 to 937 in 02768bc

  	/// Mirrors GNU's `force_symlinkat` in `force-link.c`: open the parent
  	/// directory once and operate via `*at` syscalls so a concurrent rename
  	/// of the parent cannot redirect the operation, and pick the temp name
  	/// from `/dev/urandom` so it is unguessable to other users in that
  	/// directory.

• coreutils/src/uu/mv/src/mv.rs

  Lines 945 to 948 in 02768bc

  	// GNU's template is `CuXXXXXX`: a 2-char prefix plus 6 random chars
  	// drawn from a 62-char alphabet. Modulo bias on a 256→62 mapping is
  	// ~3% per slot — irrelevant for an 8-char unguessability budget.
  	const ALPHABET: &[u8; 62] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

• dd: page-align read buffer #12143 (comment)

[sylvestre]

@collinfunk do you have some recommendations ? thanks

[sylvestre]

@collinfunk updated!