Update build-toolchain.sh and README.md for toolchain environment script changes

- Modified build-toolchain.sh to copy env.sh from the scripts directory instead of the top-level directory, ensuring proper organization.
- Updated README.md to reflect the new version of uClibc-ng and clarify the structure of the output archive, including the location of env.sh within the archive.

scripts/env.sh

@@ -0,0 +1,10 @@
+
+TOP=`pwd`
+TARGET=arm-uclinuxfdpiceabi
+CFLAGS_TOOLSET='-O2' 
+CFLAGS_TARGET='-Os -mthumb'
+CFLAGS=$CFLAGS_TOOLSET CFLAGS_FOR_TARGET=$CFLAGS_TARGET CXXFLAGS_FOR_TARGET=$CFLAGS_TARGET
+SUBARCH=armv7-m 
+SUBMODE=thumb 
+PATH=${TOP}/${TARGET}/bin:${PATH}
+