Changelog looks bad on gitbook about sourced-ce

[dpordomingo]

I think it's a good idea to show the Changelog in our docs (which is a common thing in the industry)

The problem is that GitBook does not support HTML code (only plain Markdown), so the HTML tag <details>, used to collapse the unreleased changes, is not supported.

Since we already agreed on avoiding HTML code, I'd purpose some alternatives:

• separate the unreleased changes into a new file, example: Changelog.unreleased.md, or
• since the unreleased section could not be collapsed, move it to the bottom of the CHANGELOG file.

For both alternatives, we could add a link to the unreleased changes in the top section of the original Changelog.

wdyt?

[carlosms]

Let's think about more permanent solutions in the next iterations.
For this very first release let's just hide it.

[dpordomingo]

Already hidden in my pr

[dpordomingo]

People from DP just show the unreleased stuff as another item, i.e. src-d/gitbase/CHANGELOG.md
I'd vote for that.