Added docs on how to find and set VBA codenames.
Added docs on how to find and set VBA codenames.

Issue #202.

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