[libgweather/ebassi/gtk4] docs: Begin a migration guide for libgweather-4

[Emmanuele Bassi <ebassi src gnome org>]

commit a1db116ebe1372e8534c44cca1750cc13844fdb1
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Fri Oct 15 00:24:03 2021 +0100

    docs: Begin a migration guide for libgweather-4

 doc/libgweather.toml.in |  3 +++
 doc/meson.build         |  1 +
 doc/migrating-3to4.md   | 13 +++++++++++++
 3 files changed, 17 insertions(+)
---
diff --git a/doc/libgweather.toml.in b/doc/libgweather.toml.in
index 0baa11b0..19a36134 100644
--- a/doc/libgweather.toml.in
+++ b/doc/libgweather.toml.in
@@ -35,6 +35,9 @@ base_url = "https://gitlab.gnome.org/GNOME/libgweather/-/blob/HEAD/";
 
 [extra]
 urlmap_file = "urlmap.js"
+content_files = [
+  "migrating-3to4.md",
+]
 
 [[object]]
 pattern = "DEPRECATED"
diff --git a/doc/meson.build b/doc/meson.build
index 7ee4cd0a..419f9790 100644
--- a/doc/meson.build
+++ b/doc/meson.build
@@ -17,6 +17,7 @@ if get_option('gtk_doc') and get_option('introspection')
   )
 
   gweather_content_files = [
+    'migrating-3to4.md',
   ]
 
   custom_target('libgweather-doc',
diff --git a/doc/migrating-3to4.md b/doc/migrating-3to4.md
new file mode 100644
index 00000000..b0670615
--- /dev/null
+++ b/doc/migrating-3to4.md
@@ -0,0 +1,13 @@
+Title: Migrating from GWeather 3.x to GWeather 4
+
+## Migrating from GWeather 3.x to GWeather 4
+
+GWeather 4 is a new major version that breaks API and ABI compared with
+GWeather 3.
+
+### Stop using `GWeatherLocationEntry` and `GWeatherTimezoneMenu`
+
+GWeather 4 does not provide GTK widgets for selecting a location or a time
+zone. Applications should provide their own UI, if needed, according to the
+best practices of the [GNOME human interface
+guidelines](https://developer.gnome.org/hig/).