wal: add a doc file

I agree with the rename. I will do it.
On Sep 10, 2014 8:59 PM, "Xiang Li" <notifications@github.com> wrote:

> In wal/doc.go:
>
> > +When a user has finished using a WAL it must be closed:
> > +
> > +	w.Close()
> > +
> > +WAL files are placed inside of the directory in the following format:
> > +$seq-$index.wal
> > +
> > +Periodically a user will want to "cut" the WAL and place new entries into a new
> > +file. This will increment an internal sequence number and cause a new file to
> > +be created. If the last raft index saved was 0x20 and this is the first time
> > +Cut has been called on this WAL then the sequence will increment from 0x0 to
> > +0x1. The new file will be: 0000000000000001-0000000000000020.wal
> > +
> > +At a later time a WAL can be opened at a particular raft index:
> > +
> > +	w, err := wal.OpenFromIndex("/var/lib/etcd", 0)
>
> @philips <https://github.com/philips> blake suggests to rename this to
> OpenAtIndex. I think it is better.
> What do you think?
>
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> <https://github.com/coreos/etcd/pull/1054/files#r17403240>.
>