mintro: write humman-readable JSON

Signed-off-by: Filipe Laíns <lains@riseup.net>
diff --git a/mesonbuild/mintro.py b/mesonbuild/mintro.py
index a5ce72a..c678cf7 100644
--- a/mesonbuild/mintro.py
+++ b/mesonbuild/mintro.py
@@ -592,7 +592,7 @@
         out_file = os.path.join(info_dir, f'intro-{kind}.json')
         tmp_file = os.path.join(info_dir, 'tmp_dump.json')
         with open(tmp_file, 'w', encoding='utf-8') as fp:
-            json.dump(data, fp)
+            json.dump(data, fp, indent=2)
             fp.flush() # Not sure if this is needed
         os.replace(tmp_file, out_file)
         updated_introspection_files.append(kind)