Add a web docs page explaining the API changes and how to update.

[jatkinson1000]

This PR adds a web docs page explaining the API changes and how to update following the breaking changes of #136 and #143

This can then be sent to known users to help them update.

[dorchard]

Alongside this perhaps we should bump the package number here:

FTorch/src/CMakeLists.txt

Line 4 in ac4c14f

set(PACKAGE_VERSION 0.1)

And perhaps a change to switch to semantic versioning?

[jatkinson1000]

We could, but I am not sure it carries much meaning since we haven't updated it so far...
My plans were to make a JOSS release v1.0.0 and then be more rigorous from that point.

[TomMelt]

@jatkinson1000 this is amazing. Thanks for doing this. It's really clear what the changes are and how to upgrade to the new API. Super 🚀

[jatkinson1000]

Thanks @TomMelt I will wait for Joe to have a final look over #143 and then merge this after that goes in.

I'm collating a list of users to email so please add any users you are aware of that I need to email here @dorchard @jwallwork23:

• Laura Mansfield and Stanford
• Will Chapman and NCAR
• H. Heuer and ICON
• vbalmer
• WaveWatch 3

[jwallwork23]

Very clear, nice! One optional minor comment.

[jatkinson1000]

Minor Aesthetic changes to the webpage and added a note to the README to highlight until v1.0.0.
Issue #146 opened to remind us to revert these changes after a suitable period.