docs: improve homepages

[tachyonicClock]

No description provided.

[tachyonicClock]

I felt the old home page was a little cluttered and that the description emphasises how rather than what capymoa does.

• The new page looks like this:

• The old page looks like this:

• I added PyTorch as a dependency. I did not do this earlier since it will download CUDA PyTorch by default. But the improved simplicity of installation for a user may be worth it.

• I updated the navbar:
  

• Update the installation instructions.

[tachyonicClock]

Review:

• Add online continual learning to bolded tag line.