Updating the docs

vsomeip-sys/README.md

@@ -20,4 +20,14 @@ If you are running a Linux-based OS running x86_64, it's possible these look lik
 ```
 GENERIC_CPP_STDLIB_PATH = /usr/include/c++/11
 ARCH_SPECIFIC_CPP_STDLIB_PATH=/usr/include/x86_64-linux-gnu/c++/11
-```
+```
+
+## Supplying your own vsomeip includes
+
+You may modify the build command above to include setting the environment variable:
+
+```
+VSOMEIP_INCLUDE_PATH=<path/to/vsomeip/include>
+```
+
+`VSOMEIP_INCLUDE_PATH` must point to the folder which has the `vsomeip` folder within it containing the vsomeip includes.