Added docs for position_axis.
Added docs for position_axis.

liukaijv/XlsxWriter,gechong/XlsxWriter,jmcnamara/XlsxWriter,Thhhza/XlsxWriter,jkyeung/XlsxWriter,applicationdevm/XlsxWriter,mdeemer/XlsxWriter,yaojingwu1992/XlsxWriter,jvrsantacruz/XlsxWriter,jmcnamara/XlsxWriter,gechong/XlsxWriter,Thhhza/XlsxWriter,Thhhza/XlsxWriter,seize-the-dave/XlsxWriter,gechong/XlsxWriter,applicationdevm/XlsxWriter,yaojingwu1992/XlsxWriter,seize-the-dave/XlsxWriter,liukaijv/XlsxWriter,applicationdevm/XlsxWriter,mdeemer/XlsxWriter,liukaijv/XlsxWriter,jkyeung/XlsxWriter,jmcnamara/XlsxWriter,jmcnamara/XlsxWriter,seize-the-dave/XlsxWriter,mdeemer/XlsxWriter,jkyeung/XlsxWriter,jkyeung/XlsxWriter,seize-the-dave/XlsxWriter,yaojingwu1992/XlsxWriter,jvrsantacruz/XlsxWriter,jvrsantacruz/XlsxWriter,yaojingwu1992/XlsxWriter,mdeemer/XlsxWriter,liukaijv/XlsxWriter,applicationdevm/XlsxWriter,Thhhza/XlsxWriter,gechong/XlsxWriter,jvrsantacruz/XlsxWriter