Documentation updates

[SnowHydrology]

A few issues I came across in the documentation:

• There are no install instructions. I'm on a Mac and needed to move the hfsubset executable into a directory that's part of my path for it to work (sudo mv ~/Downloads/hfsubset-v1.1.0-macos_amd64/hfsubset /usr/local/bin/hfsubset). Although this may seem obvious, it is not for everybody and should be documented.
• In several locations, the usage instructions in the README note that -r is the version flag, but it is -v
• The instructions in the README do not work for accessing non-2.2 hydrofabric versions. Per @program--, the correct syntax is: hfsubset -o ./test.gpkg -v "2.1.1" -s "nextgen" -t hl "Gages-09112500" if you wanted v2.1.1 hydrofabric data from gage number 09112500.

[mikejohnson51]

Thanks! Install directions need to move from hydrofabric docs here (@mikejohnson51). Updated flags need to move over from hfsubsetR (@mikejohnson51 / @program-- )