Add a _really_ basic README outlining building/using uClibc.

README

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+To build uClibc,
+
+1) cp ./extra/Configs/Config.<your arch> ./Config
+2) Edit ./Config for your setup.
+3) make
+4) As root, make install
+
+To compile programs with uClibc, use the gcc wrapper <arch>-uclibc-gcc
+installed in $(INSTALL_DIR)/usr/bin/ (see extra/gcc-uClibc).