Fix documentation examples in pipe.rs

Replace todo!() placeholders in documentation examples with actual working code

The examples now show how to properly create random, clocks, and sched instances

needed for WasiCtx::new() function.

Author: jiang1997

crates/wasi-common/src/pipe.rs

@@ -20,10 +20,11 @@ use std::sync::{Arc, RwLock};
 /// ```no_run
 /// use wasi_common::{pipe::ReadPipe, WasiCtx, Table};
 /// let stdin = ReadPipe::from("hello from stdin!");
-/// // Brint these instances from elsewhere (e.g. wasi-cap-std-sync):
-/// let random = todo!();
-/// let clocks = todo!();
-/// let sched = todo!();
+/// // Bring these instances from elsewhere (e.g. wasi-cap-std-sync or wasi-cap-std-tokio):
+/// use wasi_common::sync::{random_ctx, clocks_ctx, sched_ctx};
+/// let random = random_ctx();
+/// let clocks = clocks_ctx();
+/// let sched = sched_ctx();
 /// let table = Table::new();
 /// let mut ctx = WasiCtx::new(random, clocks, sched, table);
 /// ctx.set_stdin(Box::new(stdin.clone()));
@@ -116,10 +117,11 @@ impl<R: Read + Any + Send + Sync> WasiFile for ReadPipe<R> {
 /// ```no_run
 /// use wasi_common::{pipe::WritePipe, WasiCtx, Table};
 /// let stdout = WritePipe::new_in_memory();
-/// // Brint these instances from elsewhere (e.g. wasi-cap-std-sync):
-/// let random = todo!();
-/// let clocks = todo!();
-/// let sched = todo!();
+/// // Bring these instances from elsewhere (e.g. wasi-cap-std-sync or wasi-cap-std-tokio):
+/// use wasi_common::sync::{random_ctx, clocks_ctx, sched_ctx};
+/// let random = random_ctx();
+/// let clocks = clocks_ctx();
+/// let sched = sched_ctx();
 /// let table = Table::new();
 /// let mut ctx = WasiCtx::new(random, clocks, sched, table);
 /// ctx.set_stdout(Box::new(stdout.clone()));