In default config and in plugin rights I have created a PluginWriteRightCanAppend but it is not implemented.
To be able to do that, gitroot should provide an Append(path string, content string) method.
But plugin should be able to know if user has only append content in file. Maybe reuse func (repo *GitRootRepositoryWrite) GetDiff(hash plumbing.Hash, filepath string) from diff but change the return?