Update README.md

Author: giseburt

README.md

@@ -1,2 +1,7 @@
 # gcc-arm-none-eabi-archive
-This serves to archive the ARM GCC for bare-metal Cortex-M and Cortext-R, built by them or us
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+This serves to archive the ARM GCC for bare-metal Cortex-M and Cortext-R, or as ARM calls it the [GNU Arm Embedded Toolchain](https://developer.arm.com/open-source/gnu-toolchain/gnu-rm), built by them (when available) or us.
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+When we build it we use their source package and build instructions, changing as little as possible, to get the binaries for the build target only (IOW, we don't cross-compile for Windows from Raspberry Pi for the `armv7l` target).
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+