Mention possibility to build and link with wxWidgets statically (#615)

README.md

@@ -72,6 +72,10 @@ Linux:
 - Using the version of  wxWidgets from https://github.com/wxWidgets/wxWidgets.git
   - Follow the instructions to build there, but add `--enable-unicode` and
    `--disable-shared` to the `configure` step.
+  - You can also build wxWidgets as a subproject in the case that TreeSheets should be build and link statically 
+    against wxWidgets. In this case, the TreeSheets CMake project must be configured with the option
+    `TREESHEETS_WITH_STATIC_WXWIDGETS` set and with the source code of wxWidgets (including its submodules)
+    being located at `lib/wxWidgets` relative to the root of the TreeSheets source code.
 - Build with `cmake -S . -B _build -DCMAKE_BUILD_TYPE=Release` or similar.
   You can change the default installation prefix (`/usr/local`) by passing something like `-DCMAKE_INSTALL_PREFIX=/usr`.
 - Install using `sudo make -C _build install`.