Add README.

README

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+This repository provides integration scripts to build complete standalone
+SDK (with toolchain) for software development for Espressif ESP8266,
+ESP8266EX chips.
+
+Complete SDK consists of:
+
+1. Xtensa lx106 architecture toolchain (100% OpenSource), based on
+following projects:
+
+https://github.com/jcmvbkbc/crosstool-NG
+https://github.com/jcmvbkbc/gcc-xtensa
+https://github.com/jcmvbkbc/newlib-xtensa
+https://github.com/tommie/lx106-hal
+
+The sourcecode above originates from work done directly by Tensilica Inc.,
+Cadence Design Systems, Inc, or their contractors.
+
+2. ESP8266 IoT SDK from Espressif Systems. This component is only partially
+open source, some libraries provided as binary blobs. 
+
+http://bbs.espressif.com/viewforum.php?f=5
+
+OpenSource components of SDK are based on:
+
+lwIP, http://savannah.nongnu.org/projects/lwip/
+Contiki, http://www.contiki-os.org/
+axTLS, http://axtls.sourceforge.net/
+
+
+Building
+========
+
+To build standalone SDK with toolchain, you need GNU/POSIX system (Linux,
+BSD, MacOSX, Windows with Cygwin) with standard GNU development tools
+installed, like gcc, binutils, flex, bison, etc.
+
+To start build process run:
+
+    make
+
+This will download all necessary components and compile them. Once done,
+the toolchain (with Xtensa HAL library) will be available in toolchain/
+directory. Add its bin/ subdirectory to execute "xtensa-lx106-elf-gcc"
+and other tools.
+
+ESP8266 SDK will be installed in sdk/, to use it, run the compiler with
+corresponding include and lib dir flags:
+
+xtensa-lx106-elf-gcc -I$(THISDIR)/sdk/include -L$(THISDIR)/sdk/lib