docs(install): add Windows BUILD_MONAI command variants

docs/source/installation.md

@@ -110,13 +110,37 @@ or, to build with MONAI C++/CUDA extensions:
 BUILD_MONAI=1 pip install git+https://github.com/Project-MONAI/MONAI
 ```
 
+On Windows, set the environment variable with your shell syntax:
+
+```powershell
+$env:BUILD_MONAI = "1"
+pip install git+https://github.com/Project-MONAI/MONAI
+```
+
+```bat
+set BUILD_MONAI=1
+pip install git+https://github.com/Project-MONAI/MONAI
+```
+
 To build the extensions, if the system environment already has a version of Pytorch installed,
 `--no-build-isolation` might be preferred:
 
 ```bash
 BUILD_MONAI=1 pip install --no-build-isolation git+https://github.com/Project-MONAI/MONAI
 ```
 
+Windows equivalents:
+
+```powershell
+$env:BUILD_MONAI = "1"
+pip install --no-build-isolation git+https://github.com/Project-MONAI/MONAI
+```
+
+```bat
+set BUILD_MONAI=1
+pip install --no-build-isolation git+https://github.com/Project-MONAI/MONAI
+```
+
 this command will download and install the current `dev` branch of [MONAI from
 GitHub](https://github.com/Project-MONAI/MONAI).
 
@@ -147,6 +171,20 @@ BUILD_MONAI=1 pip install -e .
 BUILD_MONAI=1 CC=clang CXX=clang++ pip install -e .
 ```
 
+On Windows:
+
+```powershell
+cd MONAI/
+$env:BUILD_MONAI = "1"
+pip install -e .
+```
+
+```bat
+cd MONAI/
+set BUILD_MONAI=1
+pip install -e .
+```
+
 To uninstall the package please run:
 
 ```bash