Update tmsi documentation

doc/gh-pages/pages/documentation/scan_tmsi.md

@@ -6,4 +6,11 @@ nav_order: 13
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 # TMSI
 
-The MNE Scan TMSI plugin adds support for TMSI Refa amplifiers. The plugin is Windows only since the TMSI SDK ships for Windows operating systems. There are no additional steps needed to build the plugin. However, you need to make sure that the `TMSiSDK.dll` is present in `C:/Windows/System32/TMSiSDK.dll`. This is where the plugin will try to load the DLL from.
+The TMSI plugin is only available on the Windows operating system; the TMSI SDK is only available for that platform. Currently the TMSI plugin is not available in the compiled binary releases of MNE-CPP. To get the plugin, it is necessary to build mne_scan from source while having the tmsi drivers installed (you need to make sure that the `TMSiSDK.dll` is present in `C:/Windows/System32/TMSiSDK.dll`.). Follow the instruction in the [build guide](../development/buildguide_cmake.md). If building with the command line script, add `tmsi` after the call, like so:
+
+```
+./tools/build_project.bat tmsi
+```
+
+If building in QtCreator or calling CMake manually, add `-DWITH_TMSI=ON` to your CMake step.
+