arc: add README for architecture

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Francois Bedard <fbedard@synopsys.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>

doc/README.ARC

+Synopsys' DesignWare(r) ARC(r) Processors are a family of 32-bit CPUs
+that SoC designers can optimize for a wide range of uses, from deeply embedded
+to high-performance host applications.
+
+More information on ARC cores avaialble here:
+http://www.synopsys.com/IP/ProcessorIP/ARCProcessors/Pages/default.aspx
+
+Designers can differentiate their products by using patented configuration
+technology to tailor each ARC processor instance to meet specific performance,
+power and area requirements.
+
+The DesignWare ARC processors are also extendable, allowing designers to add
+their own custom instructions that dramatically increase performance.
+
+Synopsys' ARC processors have been used by over 170 customers worldwide who
+collectively ship more than 1 billion ARC-based chips annually.
+
+All DesignWare ARC processors utilize a 16-/32-bit ISA that provides excellent
+performance and code density for embedded and host SoC applications.
+
+The RISC microprocessors are synthesizable and can be implemented in any foundry
+or process, and are supported by a complete suite of development tools.
+
+The ARC GNU toolchain with support for all ARC Processors can be downloaded
+from here (available pre-built toolchains as well):
+
+https://github.com/foss-for-synopsys-dwc-arc-processors/toolchain/releases