Add Release Notes into Blog

[rajarshimaitra]

Currently the Blog section of the site contains few old release notes.

This issue is to propose publication of the Relase Notes in the site too with BDK release. Now that the project is getting more eyes, it will be helpful to have the latest release note in the site along with all other places.

We might wanna have a separate segment for Release too, but I think Blog is a good enough place.

[notmandatory]

I think it's be easier to keep up to-to-date if we just add a link somewhere to the GitHub releases page:
https://github.com/bitcoindevkit/bdk/releases

If we do that should it go on the top menu or the side documentation menu?

[rajarshimaitra]

I think a side menu makes more sense in this case.. Doesn't need to be at landing page top..

Could be another item in the Blog menu just redirecting to the github release link.

[notmandatory]

Adding a link to the releases page on the side menu sounds good to me.