SDL: Include README.md in the distribution archive

From a894ce4c14bc351e65ce565b60cf8e73c3923afe Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Tue, 27 Jul 2021 08:34:46 -0700
Subject: [PATCH] Include README.md in the distribution archive

---
 Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile.in b/Makefile.in
index 23c1bf1e19..5db3eea995 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -48,7 +48,7 @@ WAYLAND_SCANNER_CODE_MODE = @WAYLAND_SCANNER_CODE_MODE@
 
 INSTALL_SDL2_CONFIG = @INSTALL_SDL2_CONFIG@
 
-SRC_DIST = *.txt acinclude Android.mk autogen.sh android-project build-scripts cmake cmake_uninstall.cmake.in configure configure.ac debian docs include Makefile.* sdl2-config.cmake.in sdl2-config-version.cmake.in sdl2-config.in sdl2.m4 sdl2.pc.in SDL2.spec.in SDL2Config.cmake src test VisualC VisualC-WinRT Xcode Xcode-iOS wayland-protocols
+SRC_DIST = *.md *.txt acinclude Android.mk autogen.sh android-project build-scripts cmake cmake_uninstall.cmake.in configure configure.ac debian docs include Makefile.* sdl2-config.cmake.in sdl2-config-version.cmake.in sdl2-config.in sdl2.m4 sdl2.pc.in SDL2.spec.in SDL2Config.cmake src test VisualC VisualC-WinRT Xcode Xcode-iOS wayland-protocols
 GEN_DIST = SDL2.spec
 
 ifneq ($V,1)