x230: move splashscreen docs to common

Author: merge

common/doc/splashscreen.md

@@ -0,0 +1,13 @@
+In order to create your own splashscreen image, before building,
+overwrite the `bootsplash.jpg` with your own JPEG, using
+* "Progressive" turned off, and
+* "4:2:0 (chroma quartered)" Subsampling
+
+You can use `imagemagick` to prepare the .jpg file using:
+* `mogrify logo.jpg -interlace none <splashscreen>`
+* `mogrify logo.jpg -sampling-factor 4:2:0 <splashscreen>`
+* `convert <splashscreen> -resize 1024x768! <splashscreen> # optional, but converts image size to match screen dimensions`
+
+`ImageMagick` can also be used to convert images of another format into .jpg using the [convert](https://imagemagick.org/script/convert.php) tool.
+
+**Note**: replace `<splashscreen>` with the file name.

x230/README.md.in

@@ -273,8 +273,4 @@ for more details.
 * `./build.sh` and choose the configuration you want to build
 
 ### replace the splashscreen image
-In order to create your own splashscreen image, before building,
-overwrite the `bootsplash.jpg` with your own JPEG, using
-* "Progressive" turned off, and
-* "4:2:0 (chroma quartered)" Subsampling
-
+![[common/doc/splashscreen.md]]