doc: initialize next directory for Go 1.24

Following the "For the release team" steps in README:

	cd doc
	cp -R initial/ next
	$EDITOR next/1-intro.md

Dropped '*' from the cp -R command to avoid needing to
create an empty next directory with a separate command.

For #68545.
For #67586.

Change-Id: I25215bc35a043e0f26d4a86ffe66eb3c26348fef
Reviewed-on: https://go-review.googlesource.com/c/go/+/600177
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: dmitshur

doc/README.md

@@ -70,6 +70,6 @@ To begin the next release development cycle, populate the contents of `next`
 with those of `initial`. From the repo root:
 
     > cd doc
-    > cp -r initial/* next
+    > cp -R initial/ next
 
 Then edit `next/1-intro.md` to refer to the next version.

doc/next/1-intro.md

@@ -0,0 +1,14 @@
+<!--
+NOTE: In this document and others in this directory, the convention is to
+set fixed-width phrases with non-fixed-width spaces, as in
+`hello` `world`.
+-->
+
+<style>
+  main ul li { margin: 0.5em 0; }
+</style>
+
+## DRAFT RELEASE NOTES — Introduction to Go 1.24 {#introduction}
+
+**Go 1.24 is not yet released. These are work-in-progress release notes.
+Go 1.24 is expected to be released in February 2025.**

doc/next/2-language.md

@@ -0,0 +1,3 @@
+## Changes to the language {#language}
+
+

doc/next/3-tools.md

@@ -0,0 +1,6 @@
+## Tools {#tools}
+
+### Go command {#go-command}
+
+### Cgo {#cgo}
+

doc/next/4-runtime.md

@@ -0,0 +1 @@
+## Runtime {#runtime}

doc/next/5-toolchain.md

@@ -0,0 +1,7 @@
+## Compiler {#compiler}
+
+## Assembler {#assembler}
+
+## Linker {#linker}
+
+

doc/next/6-stdlib/0-heading.md

@@ -0,0 +1,2 @@
+## Standard library {#library}
+

doc/next/6-stdlib/99-minor/0-heading.md

@@ -0,0 +1,3 @@
+### Minor changes to the library {#minor_library_changes}
+
+

doc/next/6-stdlib/99-minor/README

@@ -0,0 +1 @@
+API changes and other small changes to the standard library go here.

doc/next/7-ports.md

@@ -0,0 +1,2 @@
+## Ports {#ports}
+