docs: Windows build docs are missing `make deploy`

[ch4ot1c]

When building for Windows (using doc/build-windows.md), I discovered the following steps were necessary but undocumented, in order to generate the installer:

sudo apt install nsis
make deploy
makensis share/setup.nsi

[LucianaMarques]

Hi there, I'd like to work on this. Is there any PR on this already?

[fanquake]

@LucianaMarques no, feel free to make the changes and open one.

[LucianaMarques]

@fanquake pull request opened! thanks

[laanwj]

The last step is not necessary see my comment here: #14744 (comment)