Releases do not say minimum version of macOS required

[peterjc]

I was curious to try contour on my main machine which is currently an old Intel Mac, which Apple no longer supports and is therefore stuck as macOS 12.7.6 "Monterey". Looking at https://github.com/contour-terminal/contour/releases it was not clear what minimum version of macOS was expected, if any. I found out by downloading and trying:

• Contour 0.5.1.7247 Darwin - requires macOS 14.0 or later
• Contour 0.4.3.6442 Darwin - requires macOS 13.0 or later
• Contour 0.4.0.6245 Darwin - requires macOS 13.0 or later
• Contour 0.3.12.262 Darwin - willing to run on macOS 12.7.6

It would be nice to add a line to the first releases where this changed, which looks like v0.4.x requiring macOS 13.0 "Ventura" or later, and v0.5.x requiring macOS 14.0 "Sonoma" or later.

Also, https://github.com/contour-terminal/contour/blob/master/README.md still says under requirements:

operating system: A recent operating system (macOS 12, ...)

That should probably now say macOS 14?