Make vcpkg MSW instructions more MSW-like

[PBfordev]

Make command line instructions for vcpgk more similar to those used
for example for nmake. The MS Windows command line does not use $ as
the command prompt and batch files are more commonly used then Unix
shell scripts.

[vadz]

Thanks, this indeed seems better to me. @NancyLi1013 any objections?

[PBfordev]

Ah, I did not realize the instructions came from the vcpkg team. Nevertheless, I still believe that these are MSW-specific instructions and the presentation in the whole file should be the same, regardless of the tool. I noticed that sometimes command line instructions in this file do not use any command prompt character. Perhaps it would be better to remove the prompt altogether from everywhere (including MSYS?) as all the commands are short single-line ones.

BTW, I also noticed an embarrassing typo in the 4th word from the end of the commit message: "then" -> "than".

[NancyLi1013]

@PBfordev and @vadz
Thanks for your suggestions and help.
No problem for me.
It might be better to make the instructions more suitable for the specific port.