add github pages site

docs/documentation/getting-started/building.md

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+To build a standalone application, use the Makefile provided in the repository.
+Go version **1.21** or higher has to be installed to build WireGuard Portal.
+If you want to re-compile the frontend, NodeJS **18** and NPM >= **9** is required.
+
+```shell
+# build the frontend (optional)
+make frontend
+
+# build the binary
+make build
+```