Update language-highlight.md

Author: trusktr

docs/language-highlight.md

@@ -8,4 +8,24 @@
 <script src="//cdn.jsdelivr.net/npm/prismjs/components/prism-php.min.js"></script>
 ```
 
+To use the new languages, make sure the code block label matches the part after `prism-` in the file name. FOr example, for `prism-bash.js` write a code block labeled with `bash` like this:
+
+````
+```bash
+echo "hello"
+```
+````
+
+?> Note that with GitHub-flavored markdown, `sh` and `bash` are effectively aliases of each other, but this is not the case with Prism. So using `sh` will not enable `bash` syntax in this case.
+
+For `prism-php.js`, it would be:
+
+````
+```php
+function getAdder(int $x): int {
+    return 123
+}
+```
+````
+
 ?> Check the [component files](https://github.com/PrismJS/prism/tree/gh-pages/components) list for more options.