update readme

Author: Conduitry

README.md

@@ -8,6 +8,7 @@ An ESLint plugin for Svelte v3 components.
 - Variable references in your template or in store auto-subscriptions are handled when linting for unused variables
 - Self-assignments are always allowed, as this is an official pattern for manually triggering reactive updates
 - Unused labels called `$` are always allowed, as this is the syntax for reactive assignments
+- Experimental opt-in linting of template expressions in addition to the script blocks
 
 ## Installation
 
@@ -79,6 +80,14 @@ This can be `true` or `false` or a function that accepts an object of attributes
 
 The default is to not ignore any styles.
 
+### `svelte3/lint-template`
+
+**Experimental! Requires at least Svelte 3.2.0!**
+
+This can be `true` or `false` or a function that accepts a file path and returns whether this plugin should also lint its template expressions.
+
+The default is to not lint any expressions in the template.
+
 ## Using the CLI
 
 It's probably a good idea to make sure you can lint from the command line before proceeding with configuring your editor.