Readd linux gnu builds, fix installation instructions

[nicmr]

Description

• e4ac9e3 removed builds for glibc / gnu linux, providing only musl libc artifacts. I think it's very convenient to users to provide gnu binaries - it's probably still the most widely used libc - so this PR adds them back, while also keeping the musl builds.
• The installation instructions are currently broken: README.md even still refers to the removed gnu artifact and to an outdated version
• The crate version in Cargo.toml was also outdated
• The name and build matrix variables of the build matrix were unused and just an abbreviation of the target variable

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Not tested

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Ramilito]

I'll create an issue to try and automate that!