Use new relative link syntax in README

See https://help.github.com/articles/relative-links-in-readmes.
Merge pull request #143 from enaeseth/patch-1

Use new relative link syntax in README
Concealcursor should be a string.
Use option g:org_indent to disable/enable indenting.
Add documentation about g:org_indent variable
Merge pull request #145 from sj5/master

Use option g:org_indent to disable/enable indenting.
Merge branch 'master' of https://github.com/jceb/vim-orgmode