CheckExistsAsync documentation

[reader-man]

Hi,
Thanks for the great project.
the "CheckExistsAsync" function does not clearly mention that it checks for a folder relative to :

FileSystem.Current.LocalStorage

e.g.

            var rootFolder = FileSystem.Current.LocalStorage;
            var exist = await rootFolder.CheckExistsAsync("DB");

and that it will not work if i give it:

            var rootFolder = FileSystem.Current.LocalStorage;

            var dbPath = PortablePath.Combine(rootFolder.Path, "DB");

            var exist = await rootFolder.CheckExistsAsync(dbPath);

as the "dbPath" is going to have a full path.

which gives a lot of headache before discovering it, at least it did for me.
Wither that, or allow the "CheckExistsAsync" to work with the passed full path if its path contained in the passed one.

[JKennedy24]

this also tripped me up. seems to be difference on different platforms from what I found