docs: create basic README.md

README.md

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+# C4EV3.Toolchain (Work-in-progress)
+
+This `arm-c4ev3-linux-uclibceabi` Toolchain consists of:
+
+* **cross-compiler:** {gcc,g++}-8.2.1 (`--with-cpu=arm926ej-s --`)
+* **libc**: uclibc-ng-1.0.31 (statically linked by default)
+* **assembler/linker**: binutils-2.31.1
+* **kernel headers**: kernel-2.6.33-rc4-sanitized
+
+It's meant for use when a recent C/C++ Toolchain is needed for the EV3,
+while still running on stock firmware.
+
+### How to build
+
+C4EV3-Toolchain is a configuration of [OSELAS.Toolchain].
+To build an [OSELAS.Toolchain], you will first need to install [PTXdist] `v2019.07.0`.
+
+Afterwards, this project can be built via:
+
+```
+ptxdist select ptxconfigs/arm-c4ev3-linux-uclibceabi_gcc-8.2.1_uclibc-ng-1.0.31_binutils-2.31.1_kernel-2.6.33-rc4-sanitized.ptxconfig
+ptxdist go -j -q
+```
+
+This will proceed to download all needed packages, build them and installs them into `/opt`.
+If you want to install elsewhere or change other configuration, you may do so via running `ptxdist menuconfig`.
+
+
+### How to use
+
+Just invoke the `arm-c4ev3-linux-uclibceabi-gcc` or `arm-c4ev3-linux-uclibceabi-g++` to compile your sources.
+You can use [ev3duder] to upload the resulting ELF binary to the EV3. It should work out of the box as resulting
+binaries are statically linked and need no supporting software on the EV3 except for the kernel.
+
+
+### FAQ
+
+- *What operating systems are supported?* So far this has only been tested on Linux. It should work on BSD as well. macOS is problematic because of outdated GNU bash.
+
+- *Why no glibc?* Building outdated low level libraries with modern tools is a hassle. Most C4EV3 programs are quite limited in what they use from the stock glibc, so dropping it in favor of a statically linked uClibc isn't a big loss.
+
+- *How to reduce binary size?* Try compiling with `-fdata-sections -ffunction-sections`
+
+[OSELAS.Toolchain]: https://www.pengutronix.de/en/software/toolchain.html
+[PTXdist]: https://ptxdist.org
+[ev3duder]: https://github.com/c4ev3/ev3duder