[Misc] Add scripts to generate witx docs.

doc/witx/.gitignore

+# SPDX-License-Identifier: Apache-2.0
+
+# ignore generated markdown files
+/*.md

utils/witx-doc/.gitignore

+# SPDX-License-Identifier: Apache-2.0
+/target
+Cargo.lock

utils/witx-doc/Cargo.toml

+[package]
+name = "witx-doc"
+version = "0.0.0"
+edition = "2018"
+
+[dependencies]
+witx = "^0.8.8"

utils/witx-doc/generate.sh

+#!/usr/bin/env bash
+# SPDX-License-Identifier: Apache-2.0
+set -x
+
+WD="$(realpath $(dirname "${BASH_SOURCE[0]}"))"
+ROOT="$(realpath $WD/../../)"
+WITX_DIR="$ROOT/doc/witx"
+
+cd $WD
+cargo build --release
+target/release/witx-doc "$WITX_DIR"

utils/witx-doc/src/main.rs

+// SPDX-License-Identifier: Apache-2.0
+use std::{
+    ffi::OsStr,
+    fs,
+    io::{self, Write},
+    path::PathBuf,
+    process,
+};
+use witx::{self, Documentation};
+
+fn main() -> io::Result<()> {
+    let arg1 = std::env::args().nth(1).expect("args 1 = witx root-dir");
+
+    let dirname = PathBuf::from(arg1);
+    let sources = fs::read_dir(dirname.as_path())?
+        .filter_map(|res| {
+            res.map_or(None, |i| {
+                let p = i.path();
+                match p.extension().and_then(OsStr::to_str) {
+                    Some("witx") => Some(p),
+                    _ => {
+                        println!("skipped {:?}", p);
+                        None
+                    }
+                }
+            })
+        })
+        .collect::<Vec<_>>();
+    println!("sources: {:?}", sources);
+
+    match witx::load(&sources) {
+        Ok(doc) => {
+            let docfile = dirname.join("docs.md");
+            println!("docfile: {:?}", docfile);
+            let mut file = fs::File::create(docfile).expect("create output file");
+            file.write_all(doc.to_md().as_bytes())
+                .expect("write output file");
+        }
+        Err(e) => {
+            eprintln!("{}", e.report());
+            process::exit(7);
+        }
+    };
+    Ok(())
+}