Doc reviews + enhancements

[dhaniram-kshirsagar]

📚 Documentation

This has been created to review overall doc changes and figure out if there are any technical or doc flow shortcomings-
Findings -

1. Add a link to custom handler doc in MAR doc
2. Provide more details around requirements.txt which is a parameter to torch-model-archive when you someone wants to install model-specific python packages

....more to be added and fixed

[deepakbabel]

Some documentations sections appear to be broken in examples section. Here are the steps that I tried:

1. Navigate to https://github.com/pytorch/serve/tree/master/examples.
   The following URL's are not updated properly:

• Serving torchvision image classification models in TorchServe
• Serving custom model with custom service handler
• Serving text classification model
• Serving object detection model
• Serving image segmentation model

Also subsection for Hugging Face Transformers is missing from the above list.

[deepakbabel]

In examples section for batch inference, there is some typos. Details below:
Navigate to https://github.com/pytorch/serve/blob/master/docs/batch_inference_with_ts.md#batch-inference-with-torchserve-using-resnet-152-model

In the "Run inference to test the model" section, the port number is missing while infering:
curl localhost/predictions/resnet-152-batch -T kitten.jpg
As the port number is not specified, it will normally default to port 80 and hence throw error while trying to run inference.