Add more platforms and differentiate arm/v8 32 and 64 bit images

[felddy]

🗣 Description

This PR adds support for linux/arm/v5 as well as differentiating the 32 and 64 bit version of arm/v8.
It also adds a platform shield to the README.

💭 Motivation and context

Moar platforms. Also my need to understand the difference between:

• linux/arm64
• linux/arm64/v8 (see the official Node image) (still not sure how they did that)
• linux/arm/v8

Platform ID	file output
linux/386	ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, for GNU/Linux 3.2.0, BuildID[xxHash]=f46b27de5c4a8a7f, with debug_info, not stripped
linux/amd64	ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), static-pie linked, for GNU/Linux 3.2.0, BuildID[xxHash]=dbd3ca47c61ce567, with debug_info, not stripped
linux/arm/v5	ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 3.2.0, BuildID[xxHash]=50f99f570c2b21c5, with debug_info, not stripped
linux/arm/v6	ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 3.2.0, BuildID[xxHash]=50f99f570c2b21c5, with debug_info, not stripped
linux/arm/v7	ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 3.2.0, BuildID[xxHash]=e463fe9bf6edd15b, with debug_info, not stripped
linux/arm/v8	ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 3.2.0, BuildID[xxHash]=e463fe9bf6edd15b, with debug_info, not stripped
linux/arm64/v8	ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, for GNU/Linux 3.7.0, BuildID[xxHash]=84097580461812b0, with debug_info, not stripped
linux/ppc64le	ELF 64-bit LSB executable, 64-bit PowerPC or cisco 7500, OpenPOWER ELF V2 ABI, version 1 (SYSV), statically linked, for GNU/Linux 3.10.0, BuildID[xxHash]=c90a09e5e87d7895, with debug_info, not stripped
linux/s390x	ELF 64-bit MSB executable, IBM S/390, version 1 (GNU/Linux), statically linked, BuildID[sha1]=dbbcd619acca47f3f4bab2a004d7d7bb12482458, for GNU/Linux 3.2.0, with debug_info, not stripped

Context:

• https://stackoverflow.com/questions/70819028/relation-between-linux-arm64-and-linux-arm64-v8-are-these-aliases-for-each-othe

🧪 Testing

Tested in CI, and development machine.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• All new and existing tests pass.