- Add copy-pasteable Arch Linux `arm-none-eabi-gcc` install line similar to Ubuntu example
- Add `arm-none-eabi-newlib` as a required package for Arch
- Reformat Ubuntu and Arch install code-blocks to catch the eye for the impatient
Arch Linux changed their packaging for [arm-none-eabi-gcc](https://www.archlinux.org/packages/community/x86_64/arm-none-eabi-gcc/) by creating [arm-none-eabi-newlib](https://www.archlinux.org/packages/community/any/arm-none-eabi-newlib/) as an optional package. Without it users will get errors about missing header files like:
```
In file included from asf4/samd51/include/samd51j19a.h:49,
from asf4/samd51/include/sam.h:38,
from ./mpconfigport.h:31,
from ../../py/mpconfig.h:45,
from ../../py/emitnx64.c:3:
/usr/lib/gcc/arm-none-eabi/9.1.0/include/stdint.h:9:16: fatal error: stdint.h: No such file or directory
9 | # include_next <stdint.h>
| ^~~~~~~~~~
compilation terminated.
```
- Added D4 and moved associated SD_CS so that they are paired within list
- Added D7 and SD_CD which is the SD Card Detect pin
- Added D8 and GREEN_LED
- Added RED_LED associated with D13
- Added Setup information regarding arm complier packages
- README - Updated to reflect that feather_m0_adalogger microSD is supported
