Add term description field

[kefengwei]

Is your feature request related to a problem? Please describe.
When we translate some text, we maybe need extra information for editor.

Describe the solution you'd like
So maybe add a description field for term, allow user add description for user.

[kidoncio]

I don't know if I do a PR but I did a fork of the project and added two features:

1 - Term context (like your suggested description)
2 - Export the files using a locale as fallback

Anyway, the code is available here:
https://github.com/kidoncio/ever-traduora

If you think it's useful I can do the PR of both features or just the PR of one of them. Please let me know about it.

[evereq]

Hi @kidoncio. We will be glad if you can raise PRs for each of those features (separate PRs if possible) and I think we will merge.

Thank you,
Ruslan