bootstd: doc: Add documentation

Add documentation for this feature, including the commands and full
devicetree bindings.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/device-tree-bindings/bootstd.txt b/doc/device-tree-bindings/bootstd.txt
index f048b9d..8706c5f 100644
--- a/doc/device-tree-bindings/bootstd.txt
+++ b/doc/device-tree-bindings/bootstd.txt
@@ -25,4 +25,12 @@
 
 		filename-prefixes = "/", "/boot/";
 		bootdev-order = "mmc2", "mmc1";
+
+		syslinux {
+			compatible = "u-boot,distro-syslinux";
+		};
+
+		efi {
+			compatible = "u-boot,distro-efi";
+		};
 	};