doc: fix ES module code blocks rendering in modules.md

The two consecutive `mjs` code blocks in the "Loading ECMAScript
modules using require()" section were being incorrectly grouped
into a CJS/ESM toggle tab by doc-kit's highlighter. Add text
between the two code blocks so they render as independent code
blocks.

Author: okuryu

doc/api/modules.md

@@ -217,13 +217,15 @@ return the [module namespace object][]. In this case it is similar to dynamic
 `import()` but is run synchronously and returns the name space object
 directly.
 
-With the following ES Modules:
+With the following ES module `distance.mjs`:
 
 ```mjs
 // distance.mjs
 export function distance(a, b) { return Math.sqrt((b.x - a.x) ** 2 + (b.y - a.y) ** 2); }
 ```
 
+`point.mjs`:
+
 ```mjs
 // point.mjs
 export default class Point {