Fix the local doc build

README.markdown

@@ -42,4 +42,10 @@ $ composer install
 $ php build.php
 ```
 
-Now you can browse the docs at `_build/output/index.html`
+After generating docs, serve them with the internal PHP server:
+
+```bash
+$ php -S localhost:8000 -t output/
+```
+
+Browse `http://localhost:8000` to read the docs.

_build/build.php

@@ -46,6 +46,12 @@
         $result = (new DocBuilder())->build($buildConfig);
 
         if ($result->isSuccessful()) {
+            // fix assets URLs to make them absolute (otherwise, they don't work in subdirectories)
+            foreach (glob($outputDir.'/**/*.html') as $htmlFilePath) {
+                $htmlContents = file_get_contents($htmlFilePath);
+                file_put_contents($htmlFilePath, str_replace('href="assets/', 'href="/assets/', $htmlContents));
+            }
+
             $io->success(sprintf("The Symfony Docs were successfully built at %s", realpath($outputDir)));
         } else {
             $io->error(sprintf("There were some errors while building the docs:\n\n%s\n", $result->getErrorTrace()));