docs: add note for case-sensitive file systems

Author: kenjis

user_guide_src/source/concepts/autoloader.rst

@@ -30,6 +30,12 @@ they work in sequence and don't get in each other's way.
 The autoloader is always active, being registered with ``spl_autoload_register()`` at the
 beginning of the framework's execution.
 
+.. important:: You should always be careful about the case of filenames. Many
+    developers develop on case-insensitive file systems on Windows or macOS.
+    However, most server environments use case-sensitive file systems. If the
+    file name case is incorrect, the autoloader cannot find the file on the
+    server.
+
 Configuration
 *************
 

user_guide_src/source/tutorial/static_pages.rst

@@ -19,6 +19,12 @@ Let's Make our First Controller
 Create a file at **app/Controllers/Pages.php** with the following
 code.
 
+.. important:: You should always be careful about the case of filenames. Many
+    developers develop on case-insensitive file systems on Windows or macOS.
+    However, most server environments use case-sensitive file systems. If the
+    file name case is incorrect, code that works locally will not work on the
+    server.
+
 .. literalinclude:: static_pages/001.php
 
 You have created a class named ``Pages``, with a ``view()`` method that accepts