add link to gtk embedding cookbook to website

[tacaswell]

Include a link to https://github.com/spiessbuerger/GTK3-Matplotlib-Cookbook on the website

@spiessbuerger What is your preferred link?

Tagged as 1.5.x as it looks like it is still a work in progress.

[tobias47n9e]

I think linking to Github is fine. But waiting for 1.5 sounds reasonable. My programming career only dates back to March, so I still need to figure out stuff and work on the examples. When I am finished with the examples I will ask for some code reviews and then we could do a link.

[fariza]

I think this is dead, no changes in the cookbook since dec 2014. Should we close?

[efiring]

Thanks for checking this, @fariza.

[fariza]

you're welcome. Glad could help