Add note for Windows to set Boost_INCLUDE_DIR (#2554)

* Add note to for Windows to set `Boost_INCLUDE_DIR`

* Update docs/user-guide/installation/windows.md

Co-authored-by: Philip Top <[email protected]>

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: Philip Top <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

docs/user-guide/installation/windows.md

@@ -119,7 +119,7 @@ Studio version should match the version of the Boost libraries you are using.
 
 If you installed Boost into the root of the C or D drives with the
 default location (or the `BOOST_INSTALL_PATH` environment variable has been set), CMake should automatically detect their location. Otherwise the
-location will need to be manually given to CMake.
+location will need to be manually given to CMake through `Boost_INCLUDE_DIR`. This should be used if the Boost version is new and not known to HELICS or you want to be explicit about which boost folder to use.
 NOTE: CMake 3.14 and later separate the architecture into a separate field for the generator
 
 A basic call with `cmake` using Visual Studio 2022 on a 64bit Windows machine and installing to a folder called `install` inside the repository would be: