firmware version printing

[coelner]

The returned firmware version is not directly correlated to the github release page.

/usr/bin/solo2 app admin version
1:20200101.9

https://github.com/solokeys/solo2/tags
1.0.9 ec57c12

Maybe an explanation about the firmware string and a check before updating, if those are matching could be helpful

[Edit] related to: #29

and here: https://github.com/lpc55/lpc55-host/blob/b3fdcc8509facaf9be2151d90203f9e0c30702d7/src/secure_binary.rs#L939

/// Example: `1:20210624.0`
    pub fn to_calver(&self) -> String {
        format!("{}:{}.{}", self.major, self.minor_as_date().format("%Y%m%d"), self.patch)
    }