Fix: README.md

[kat0h]

When a source returns multiple identical candidates, ddc will merge the candidates. Use the dup option because it may make the snippet unusable This problem occurs in the fllowing case

Japanese ソースが複数の同じ候補を返したときddcは候補をマージします。 スニペットが使えなくなる可能性があるため、dupオプションを利用します これは下記の様な場合に発生します

[shun]

@kat0h Thanks for your PR. However, I'm hesitating to merge this. Because it is depends on language. I'm not sure this option is better for all of languages. If we add this option for readme and help, almost user set this in my opinion. I can't say which is better.

But this is good realization ! So, I suggest to add extra description like below. How do you think ?

Configuration

    call ddc#custom#patch_global('sources', ['vim-lsp'])
    call ddc#custom#patch_global('sourceOptions', {
        \ 'vim-lsp': {
        \   'matchers': ['matcher_head'],
        \   'mark': 'lsp',
        \ },
        \ })

ddc.vim remove duplicated keyword by default.
If you want to list up both of them, please add `'dup': v:true` .

[kat0h]

Sorry for the late reply.

I think adding a description of the options is a good idea. I've created a commit to add the explanation and force pushed it. Can you please check it?

[shun]

Thank you !