Updated FreeRTOS-Rust Linux setup instruction information in README doc

[jdharuman]

Overview

Why do we need this change?
The FreeRTOS Rust Linux machine setup instructions in the README were outdated or unclear. Updating them ensures accurate and up-to-date guidance for setting up and running the project.

What has changed?

• Updated the README with revised FreeRTOS Rust Linux machine setup instructions.
• Included additional details and clarifications where necessary.
• Changed the signature of set_on_assert() from taking a mutable reference (&mut self) to an immutable reference (&self)

11 |     unsafe {
   |     ^^^^^^ unnecessary `unsafe` block
   |
   = note: `#[warn(unused_unsafe)]` on by default

error[E0596]: cannot borrow immutable static item `FREERTOS_HOOKS` as mutable
  --> freertos-rust-examples/examples/linux/main.rs:12:9
   |
12 |         FREERTOS_HOOKS.set_on_assert(|| { println!("Assert hook called") });
   |         ^^^^^^^^^^^^^^ cannot borrow as mutable

For more information about this error, try `rustc --explain E0596`.
warning: `freertos-rust-examples` (example "linux") generated 1 warning

• Ensured that the callback functionality remains intact, with the hook being callable through the do_on_assert() method when an assertion occurs.

Testing

• Linux
  Linux console output:

~/git/FreeRTOS-rust user/jdharum..p-doc-update !1 > cargo run --example linux                                                         py platform

warning: freertos-rust-examples@0.1.1: /home/jayachandran/git/FreeRTOS-rust/freertos-rust/src/freertos/shim.c: In function 'freertos_rs_isr_yield':
warning: freertos-rust-examples@0.1.1: /home/jayachandran/git/FreeRTOS-rust/freertos-rust/src/freertos/shim.c:282:9: warning: implicit declaration of function 'portYIELD_FROM_ISR' [-Wimplicit-function-declaration]
warning: freertos-rust-examples@0.1.1:   282 |         portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
warning: freertos-rust-examples@0.1.1:       |         ^~~~~~~~~~~~~~~~~~
   Compiling freertos-rust-examples v0.1.1 (/home/jayachandran/git/FreeRTOS-rust/freertos-rust-examples)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.09s
     Running `target/debug/examples/linux`
Boxed int '15' (allocator test)
Starting FreeRTOS app ...
Task registered
Starting scheduler
Timer Resolution for Run TimeStats is 100 ticks per second.
Hello from Task! 0
Hello from Task! 1
Hello from Task! 2
Hello from Task! 3
Hello from Task! 4
Hello from Task! 5
Hello from Task! 6
^C

[jdharuman]

@niondir @apullin @CaseySanchez @reitermarkus Could you please review the PR?