Add build instructions for linux, fix some cmake issues

README.md

@@ -1 +1,36 @@
-# BeamNG-MP-Server
+# BeamNG-MP-Server
+
+## Unix specific build instructions
+
+1. You need boost >= 1.70.0
+
+Check with your ditro's package manager whether it provides this. If it does, you should use that. 
+
+
+If it doesnt provide it or you want to link it statically (like we do with our releases), then you have to do this:
+
+download the latest boost source code.
+Then, go to the downloaded directory and run
+```sh
+b2 link=static runtime-link=static threading=multi
+```
+And then either symlink, edit CMakeLists to find it, or simply run
+```sh
+b2 link=static runtime-link=static threading=multi install
+```
+(warning: installs boost into your system, you might not want this).
+
+Then on invocation of cmake, ensure that you define `Boost_USE_STATIC_RUNTIME=ON`.
+
+
+2. Building
+
+Run cmake, and then make.
+
+Example:
+
+```bash
+~/src/Server $ cmake -S . -B bin -DCMAKE_BUILD_TYPE=Release
+...
+~/src/Server $ make -C bin -j 5
+```