Fix link command in readme

Previously the ln command used in the instructions was trying to make a
link relative to the .vim directory, whic doesn't work because the link
is in the parent directory. This commit links relative to the parent and
the link is fixed.
Fix autocommand for jumping to the first line in commit message

Commit aee81a01895d3e483d643d94a867e4dcd5b8a99f added an ftplugin file
to jump to the first line of the file when editing a git commit message,
but this was always being run before the line number was recalled, so it
was overridden. This command moves the cursor later and now it works.
Check speeddating is loaded before adding new formats