docs: basic documentation on creating themes.

#129

README.md

@@ -12,7 +12,8 @@ music collection from any browser or mobile device. It's like your personal Spot
 __Any feedback is welcome!__ If you need/want a new feature, find a bug or think of any way to improve Navidrome, 
 please fill a [GitHub issue](https://github.com/deluan/navidrome/issues) or join the discussion in our 
 [Subreddit](https://www.reddit.com/r/navidrome/). If you want to contribute to the project in any other way 
-(ui/backend dev, translations, themes), please join the chat in our [Discord server](https://discord.gg/xh7j7yF). 
+(ui/backend dev, translations, [themes](ui/src/themes/README.md)), please join the chat in our 
+[Discord server](https://discord.gg/xh7j7yF). 
 
 
 ## Features

ui/src/themes/README.md

@@ -0,0 +1,20 @@
+## Creating New Themes
+
+Themes in Navidrome are simple [Material-UI themes](https://material-ui.com/customization/theming/). They are basic JS 
+objects, that allow you to override almost every aspect of Navidrome's UI.
+
+#### Steps to create a new theme:
+
+1) Create a new JS file in this folder that exports an object containing your theme. Create the theme based on the 
+ReactAdmin/Material UI documentation below. See the existing themes for examples. 
+2) Add a `themeName` property to your theme. This will be displayed in the theme selector
+3) Add your new theme to the `ui/src/themes/index.js` file
+4) Start the application, your new theme should now appear as an option in the theme selector
+
+Before submitting a pull request to include your theme in Navidrome, please test your theme thoroughly and make sure 
+it is formated with the [Prettier](https://prettier.io/) rules found in the project (`ui/src/.prettierrc.js`)
+
+#### Resources for Material-UI theming
+
+* Start reading [ReactAdmin documentation](https://marmelab.com/react-admin/Theming.html#writing-a-custom-theme)
+* Color Tool: https://material-ui.com/customization/color/#official-color-tool