Ignore *.bin (for Jujutsu's sake)

I will add this again later, [once it is supported][issue]. In the meantime,
though, I will ignore it from Jujutsu's POV, but force add it from Git's POV
so that it ends up in the repo from a Git(Hub) perspective without confusing
Jujustu.

[issue]: martinvonz/jj#80

.gitignore

@@ -31,3 +31,8 @@ Icon
 Network Trash Folder
 Temporary Items
 .apdisk
+
+# Binaries
+## Note: special handling here for Jujutsu for the moment! This ignores the
+## binary file for syntaxes, but I forcibly override that for Git!
+*.bin