Add log.showSignatrue = true to ~/.config/git/config

Moved my ~/.gitconfig to ~/.config/git/config to have a sane location to
collect git related global configs.

Added ~/.config/git/allowed_signers and configured
`gpg.ssh.allowedSignersFile' in ~/.config/git/config to have the correct
output of `git log --show-signatures'

git/allowed_signers

@@ -0,0 +1 @@
+c47@nixre.net ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAINKnoeiitP79Mp/DUSK86DGaH09H44U2QtDSB+J6rM6R c47@ferret

git/config

@@ -6,3 +6,7 @@
 
 [includeIf "gitdir:~/gits/priv/"]
 	path = ~/gits/priv/.gitconfig
+[gpg "ssh"]
+	allowedSignersFile = ~/.config/git/allowed_signers
+[log]
+	showSignature = true