update README to show R Pi 3 model B+ testing

README.txt

@@ -22,7 +22,8 @@
     pipeline).
 -   Support for server behind a firewall.
 -   Raspberry Pi support **both with and without hardware video
-    decoding** by the Broadcom GPU. *Tested on Raspberry Pi 4 Model B.*
+    decoding** by the Broadcom GPU. *Tested on Raspberry Pi 4 Model B
+    and Pi 3 model B+.*
 -   Support for running on Microsoft Windows (builds with the MinGW-64
     compiler in the unix-like MSYS2 environment).
 
@@ -418,7 +419,7 @@ plugin. If your system uses the Wayland compositor for graphics, use
 "`uxplay -vs waylandsink`".** See [Usage](#usage) for more run-time
 options.
 
-### **Special instructions for Raspberry Pi (tested on R Pi 4 model B 8GB)**:
+### **Special instructions for Raspberry Pi (tested on R Pi 4 model B 8GB and R Pi 3 model B+)**:
 
 -   If you use the software-only (h264) video-decoding UxPlay option
     `-avdec`, you also need option `-vsync`to keep audio and video
@@ -437,6 +438,13 @@ options.
     provide it: **without this kernel module, UxPlay cannot use the
     decoding firmware in the GPU.**
 
+For use of the GPU, use raspi-config "Performance Options" (on Raspberry
+Pi OS, use a similar tool on other distributions) to allocate sufficient
+memory for the GPU (on R. Pi 3 model B+, the maximum (256MB) is
+suggested). Even with GPU video decoding, some frames may be dropped by
+the lower-power 3 B+, so the -vsync option (introduced in UxPlay-1.63)
+that uses timestamps to synchronize audio and video is needed.
+
 -   The plugin in the latest GStreamer-1.22 release works well, but
     older releases of GStreamer will not work unless patched with
     backports from GStreamer-1.22. Raspberry Pi OS (Bullseye) now has a