docs: update rust toolchain. cargo-ndk requires 1.86

Author: sneurlax

docs/building.md

@@ -213,11 +213,11 @@ brew install brotli cairo coreutils gdbm gettext glib gmp libevent libidn2 libng
 ```
 <!-- TODO: determine which of the above list are not needed at all. -->
 
-Download and install [Rust](https://www.rust-lang.org/tools/install).  [Rustup](https://rustup.rs/) is recommended for Rust setup.  Use `rustc` to confirm successful installation.  Install toolchains 1.81.0 and 1.85.1 and `cbindgen` and `cargo-lipo` too.  You will also have to add the platform target(s) `aarch64-apple-ios` and/or `aarch64-apple-darwin`.  You can use the command(s):
+Download and install [Rust](https://www.rust-lang.org/tools/install).  [Rustup](https://rustup.rs/) is recommended for Rust setup.  Use `rustc` to confirm successful installation.  Install toolchains 1.81.0, 1.85.1, and 1.86.0, as well as `cbindgen` and `cargo-lipo` too.  You will also have to add the platform target(s) `aarch64-apple-ios` and/or `aarch64-apple-darwin`.  You can use the command(s):
 ```
 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
 source ~/.bashrc 
-rustup install 1.85.1 1.81.0
+rustup install 1.86.0 1.85.1 1.81.0
 rustup default 1.85.1
 cargo install cargo-ndk
 cargo install cbindgen cargo-lipo
@@ -309,7 +309,7 @@ Run `flutter doctor` in PowerShell to confirm its installation.
 ### Rust
 Install [Rust](https://www.rust-lang.org/tools/install) on the Windows host (not in WSL2).  Download the installer from [rustup.rs](https://rustup.rs), make sure it works on the commandline (you may need to open a new terminal), and install the following versions:
 ```
-rustup install 1.85.1 1.81.0
+rustup install 1.86.0 1.85.1 1.81.0
 rustup default 1.85.1
 cargo install cargo-ndk
 ```