docs: programming-language: add Rust programming language section

Following the C text in the file, add a mention about the Rust
programming language, the currently supported compiler and
the edition used (similar to the "dialect" mention for C).

Similarly, add a mention about the unstable features used (similar
to the "extensions" mentions for C).

In addition, add some links to complement the information.

Signed-off-by: Miguel Ojeda <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/process/programming-language.rst

···
 
 Please refer to ``include/linux/compiler_attributes.h`` for more information.
 
+Rust
+----
+
+The kernel has experimental support for the Rust programming language
+[rust-language]_ under ``CONFIG_RUST``. It is compiled with ``rustc`` [rustc]_
+under ``--edition=2021`` [rust-editions]_. Editions are a way to introduce
+small changes to the language that are not backwards compatible.
+
+On top of that, some unstable features [rust-unstable-features]_ are used in
+the kernel. Unstable features may change in the future, thus it is an important
+goal to reach a point where only stable features are used.
+
+Please refer to Documentation/rust/index.rst for more information.
+
 .. [c-language] http://www.open-std.org/jtc1/sc22/wg14/www/standards
 .. [gcc] https://gcc.gnu.org
 .. [clang] https://clang.llvm.org
···
 .. [gnu-extensions] https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
 .. [gcc-attribute-syntax] https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
 .. [n2049] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
-
+.. [rust-language] https://www.rust-lang.org
+.. [rustc] https://doc.rust-lang.org/rustc/
+.. [rust-editions] https://doc.rust-lang.org/edition-guide/editions/
+.. [rust-unstable-features] https://github.com/Rust-for-Linux/linux/issues/2