target/loongarch: Add README

This patch gives an introduction to the LoongArch target.

Signed-off-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220606124333.2060567-2-yangxiaojuan@loongson.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

MAINTAINERS

@@ -212,6 +212,12 @@ S: Maintained
 F: target/hppa/
 F: disas/hppa.c
 
+LoongArch TCG CPUs
+M: Song Gao <gaosong@loongson.cn>
+M: Xiaojuan Yang <yangxiaojuan@loongson.cn>
+S: Maintained
+F: target/loongarch/
+
 M68K TCG CPUs
 M: Laurent Vivier <laurent@vivier.eu>
 S: Maintained

target/loongarch/README

+- Introduction
+
+  LoongArch is the general processor architecture of Loongson.
+
+  The following versions of the LoongArch core are supported
+    core: 3A5000
+    https://github.com/loongson/LoongArch-Documentation/releases/download/2021.08.17/LoongArch-Vol1-v1.00-EN.pdf
+
+  We can get the latest loongarch documents at https://github.com/loongson/LoongArch-Documentation/tags.
+