Add Windows installation

[mabelzhang]

Partially addresses gazebosim/docs#117

Moved Documentation and Testing sections from the installation tutorial back to README - looks like a mistake that they were moved before. These two sections stayed in the README for other libraries.

One of the dependencies, libignition-rendering, is not yet on conda-forge and needs to be installed from source.
libignition-gui is also not on conda-forge, so we don't have binary install instructions for Windows in this PR.
Both libraries need to be added to conda-forge.

[codecov]

Codecov Report

Merging #161 (194080b) into ign-gui4 (016cd32) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           ign-gui4     #161   +/-   ##
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  Coverage     61.57%   61.57%           
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  Files            21       21           
  Lines          2790     2790           
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  Hits           1718     1718           
  Misses         1072     1072           

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[JShep1]

Small verbiage nit

[JShep1]

Suggested change

	Before ``ign-rendering`` becomes available on conda-forge, we need to build it from source and specify the path containing ``ignition-rendering<#>-config.cmake`` and ``ignition-rendering<#>-ogre-config.cmake`` in ``CMAKE_PREFIX_PATH``. That path could be ``ign-rendering-install-path\lib\cmake``, for example.
	As``ign-rendering`` is not available on conda-forge, we need to build it from source and specify the path containing ``ignition-rendering<#>-config.cmake`` and ``ignition-rendering<#>-ogre-config.cmake`` in ``CMAKE_PREFIX_PATH``. That path could be ``ign-rendering-install-path\lib\cmake``, for example.

[chapulina]

Moved Documentation and Testing sections from the installation tutorial back to README - looks like a mistake that they were moved before

I think I did that on purpose on #127 because they seemed out of place in the README. A README user had no context for generating docs or running tests... But I think that you are adding enough context in this PR. Maybe we can consider moving those to their own tutorials in the future. I think the README could be more focused on highlighting features and quick onboarding, and specific development details can be left to tutorials.

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Thanks for the PR. Just curious, did you try running ign gui? Does it work? How about the 3D scene plugin (ign gui -c examples/config/scene3d.config)?

[JShep1]

Closing to retarget at Citadel. #168

[JShep1]

Thanks for the PR. Just curious, did you try running ign gui? Does it work? How about the 3D scene plugin (ign gui -c examples/config/scene3d.config)?

For visibility, I tested this out by attempting to run a few examples and Qt crashed every time, for what it's worth, here is the error message in case this may be relevant later:

(test_ws) C:\Users\asus\test-ws\src\ign-gui\examples\standalone\window\build\Release>window.exe
Hello, GUI!
qt.qpa.plugin: Could not find the Qt platform plugin "windows" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Not sure if this may be a local issue or if reinstalling Qt would actually work, it could also be some sort of issue with the version of Qt that conda-forge brings in.