doc/README: documents and readme for NDS32 arch

Documents and READMEs for NDS32 architecture.
It patch also provides usage of SoC AG101 and board ADP-AG101.

Signed-off-by: Macpaul Lin <macpaul@andestech.com>
diff --git a/doc/README.standalone b/doc/README.standalone
index 6e6b65f..2be5f27 100644
--- a/doc/README.standalone
+++ b/doc/README.standalone
@@ -56,6 +56,7 @@
 	ARM		0x0c100000	0x0c100000
 	MIPS		0x80200000	0x80200000
 	Blackfin	0x00001000	0x00001000
+	NDS32		0x00300000	0x00300000
 	Nios II		0x02000000	0x02000000
 
    For example, the "hello world" application may be loaded and