Add a notice to the top of all nostarch snapshots

Hopefully directing pull request authors to src, where edits should be
made.

nostarch/chapter02.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter03.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter04.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter05.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter06.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter08.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter09.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter10.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter11.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter12.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

nostarch/chapter14.md

@@ -1,3 +1,8 @@
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
 
 [TOC]
 

tools/src/bin/concat_chapters.rs

@@ -91,7 +91,16 @@ fn concat_files(
 ) -> io::Result<()> {
     println!("Concatenating into {}:", target_path.to_string_lossy());
     let mut target = File::create(target_path)?;
-    target.write_all(b"\n[TOC]\n")?;
+
+    write!(target, "\
+<!-- DO NOT EDIT THIS FILE.
+
+This file is periodically generated from the content in the `/src/`
+directory, so all fixes need to be made in `/src/`.
+-->
+
+[TOC]
+")?;
 
     for path in source_paths {
         println!("  {}", path.to_string_lossy());