docs/migrating.adoc: document static JS library

This patch adds information on how to provides static JS libraries in
Buildroot with the release of the 2025.08.x version.

Because the way JavaScript project development is working the chances that your
project is using the same version of the buildroot package, and you provide
this library from `/var/www` to your users is actually really low ...

If you want to bundle JavaScript libraries in your project you should probably
either use a cdn, handle the package version and location of your choice in
your external or overlay, or just bundle it in your assets from a NPM workflow
to benefit from some minifications from your bundler.

Historically many of those JavaScript libraries were added in the 2010 eras
where it could make sense for them to be part of Buildroot.

Most of them are also way outdated/not maintained.

For more informations see https://elinux.org/Buildroot:DeveloperDaysELCE2025

Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

docs/manual/migrating.adoc

@@ -228,3 +228,17 @@ your kernel or use an alternative network manager.
 In 2025.11, the +FOO_INSTALL_BINS+ variable for golang packages is no longer
 supported; the list of binaries to install is automatically derived from
 the +FOO_BUILD_TARGETS+ variable.
+
+[[migrating-js-libs]]
+=== Migration to 2026.02
+
+Starting 2025.08, JavaScript libraries that were just copied to `/var/www` on
+the target filesystem are not part of the Buildroot packages.
+If you want to provide such libraries either:
+
+- Use a CDN to target the library version of your choice.
+- Serve it by adding the package to your external and installing the content to
+  the destination of your choice
+- Serve it by adding the library to your overlay.
+- Install the libraries from your project with NPM and bundle with a JavaScript
+  bundler.