docs: update v4-migration-guide.md

v4/v4-migration-guide.md

@@ -3,12 +3,15 @@
 **IMPORTANT** The Hugo version was bumped to `v0.110.0 extended`. Therefore, you should upgrade Hugo in your local
 development environment and, if necessary, in the corresponding deployment configuration file.
 
+### Site Configuration File
+Rename the site's configuration file from `config.toml` to `hugo.toml`.
+
 ### Theme Installation Options
 
-Depending on your chosen theme installation option, update the theme property in the `config.toml` file as follows:
+Depending on your chosen theme installation option, update the theme property in the `hugo.toml` file as follows:
 
 ```toml
-# Option 1 (recommended) : adding the theme as a Hugo module
+# Option 1 (recommended): adding the theme as a Hugo module
 theme = "github.com/Lednerb/bilberry-hugo-theme/v4"
 
 # Options 2 and 3: cloning/copying the theme files
@@ -34,7 +37,7 @@ guide for customization options.
 In `v3`, color and font customizations were handled directly in the `assets/sass/_variables.scss` file. In v4,
 the `_variables.scss` file no longer exists and such customization is done in the `config.toml` by defining
 corresponding parameters from the `assets/sass/theme.scss` file, for example, `baseColor`, `headlineFont` etc.
-Therefore, any changes you made in `_variables.scss` file should be ported to your site's configuration file. Read
+Therefore, any changes you made in `_variables.scss` file should be ported to your site's configuration file `hugo.toml`. Read
 the [Colors and Fonts](README.md#colors-and-fonts) section in the `v4` **README** guide for more details.
 
 ### Image Modal Zoom