Document minimum Mac OS version is 10.10

[follower]

FYI attempting to run lazygit on Mac OS X 10.9 fails with both 64-bit & 32-bit builds:

# Darwin_x86_64
$ lazygit_0.20.2_Darwin_x86_64/lazygit 
dyld: Symbol not found: _fdopendir$INODE64
  Referenced from: /<path>/lazygit_0.20.2_Darwin_x86_64/lazygit
  Expected in: flat namespace

Trace/BPT trap: 5

# Darwin_32-bit
$ lazygit_0.20.2_Darwin_32-bit/lazygit 
dyld: Symbol not found: _fdopendir$INODE64$UNIX2003
  Referenced from: /<path>/lazygit_0.20.2_Darwin_32-bit/lazygit
  Expected in: flat namespace

Trace/BPT trap: 5

It appears this is because Go 1.13 only supports macOS version 10.10+.

It would be good if the ReadMe/Release Notes specified the minimum Mac OS version as 10.10 (or whatever the current minimum Go-supported OS version is).

Also, I think this means that there's no point in have a 32-bit build available as I think the last 32-bit only Mac OS X was 10.7/Snow Leopard?

[jesseduffield]

good pickup, this is indeed something we should add to the readme