Fix v0.4 references in WSInfer docs, update extension installation instructions

[petebankhead]

e.g. see

qupath-docs/docs/deep/wsinfer.md

Lines 13 to 18 in 132a842

	## Requirements
	- QuPath [version 0.4](https://qupath.github.io/) (installation instructions [here](https://qupath.readthedocs.io/en/0.4/docs/intro/installation.html)).
	- At least one whole slide image
	- [WSInfer QuPath Extension](https://github.com/qupath/qupath-extension-wsinfer/releases)
	- PyTorch (this can be downloaded while using the extension)

Should update for v0.5, with benchmarks as described at

• benchmarking qupath-wsinfer #89

[petebankhead]

When changing this, should also update the extension installation instructions to reference the extension manager (rather than drag & drop).