README: Document custom themes

README.md

@@ -79,17 +79,45 @@ app that triggered it crashes.
 
 ## Feedback theme
 Events are then mapped to a specific type of feedback (sound, led, vibra) via a
-device specific theme (since devices have different capabilities).
+device specific theme - since devices have different capabilities and
+different users different needs.
 
 Feedbackd is shipped with a default theme `default.json`.
-You can add your own themes in one of two ways:
+You can add your own themes in multiple ways:
 
 1. By exporting an environment variable `FEEDBACK_THEME` with a path to a
    valid theme file (not recommended, use for testing only), or
 2. By creating a theme file under `$XDG_CONFIG_HOME/feedbackd/themes/default.json`.
    If `XDG_CONFIG_HOME` environment variable is not set or empty, it will
    default to `$HOME/.config`, or
-3. By adding your theme file to one of the folders in the `XDG_DATA_DIRS`
+3. By creating a theme file under `$XDG_CONFIG_HOME/feedbackd/themes/custom.json`.
+   You only specify the values you want to change in that theme and add an entry
+   ```json
+   {
+      "name: "custom"
+      "parent-theme": "default"
+	  "profiles" : [
+	   ...(entries you want to change go here)...
+	   ]
+   }
+   ```
+   next to the `name` entry in. This has the upside that your theme
+   gets way smaller and that new entries added to the default theme
+   will automatically be used by your theme too. See
+   [here](./tests/data/user-config/feedbackd/themes/custom.json) for
+   an example. Once you have the file in place, tell feedbackd the
+   them you want to use:
+
+        gsettings set org.sigxcpu.feedbackd theme custom
+
+   When you want to go back to the default theme just do:
+
+        gsettings reset org.sigxcpu.feedbackd theme
+
+   Note that you can name your theme as you wish but avoid theme names
+   starting with `__` or `$` as this namespace is reserved.
+
+4. By adding your theme file to one of the folders in the `XDG_DATA_DIRS`
    environment variable, appended with `feedbackd/themes/`. This folder isn't
    created automatically, so you have to create it yourself. Here's an example:
    ```bash