Suggest changes to README before final version

[thao-do]

1. Attach the word "plugin" in whenever it says "Allen Cell Segmenter ML" as it's the napari plugin and not the original Allen Cell & Structure Segmenter code base.
2. napari is always lower-case
3. Under "What is Allen Cell Seg..." >> "deep learning-based model.." change to to "A deep-learning based segmentation napari plugin" - don't know yet what a good word to go there
4. An explanation of "inference"
5. Briefly explain what MegaSeg models are and why they're included, and also link to MegaSeg if that's available
6. Markdown text styling is not the best to show content hierarchy but I can live with it (until there is a better way...)
7. Image legend should be start with "Fig. #" or "Image:" and should have a different text format other than Quote
8. the PyTorch installation example can refer to the image preceding it, right now they looks like two separate things but what the screen-capture image shows is the details of the example
9. Can break step 2 of the Post-installation to Step 2: Pytorch Installation and Step 3: Check if your GPU is detected by PyTorch (either if you know you have PyTorch installed already, or you just install it following the guide)
10. In "Running the plugin" section, there is a step user has to go through in between launching the plugin for the first time and downloading the models - the set Home Directory step. This might not be necessary to say the step exactly, but it might help to mention it briefly, maybe like "After launching and setting up the plugin, to use the MegaSeg models in the plugin, you can download..."
11. Make sure the final model names are correct
12. This is down the line, but we need reminder to update the end of this by linking it to the documentation.

[thao-do]

@gamlinc do you want to add your edits here too?