Added some documentation for steps on how to update a resource.

doc/update_resources.md

@@ -0,0 +1,16 @@
+# Update shipped third party resources
+
+## Eigen
+
+In Eigen, we have adapted `SparseLU` to work with scalar types that do not default construct from a double (like CLN numbers) or that do not have an operator< or std::abs
+
+To update the Eigen version, just change the corresponding commit hash in `$STORM_DIR/resources/3rdparty/CmakeLists.txt`.
+Check whether the patch located at `$STORM_DIR/resources/3rdparty/patches/eigen.patch` can be applied without issues (in particular check for changes in `Eigen/src/SparseLU/`)
+
+In case a new patch needs to be created follow these steps:
+
+1. Clone `https://gitlab.com/libeigen/eigen.git` to `$STORM_DIR/resources/3rdparty/` and checkout the corresponding commit
+2. Checkout a new branch
+3. Apply the old patch via `git apply $STORM_DIR/resources/3rdparty/patches/eigen.patch`
+4. Resolve issues, make changes, and commit them
+5. Create a new patch file via `git format-patch <tag> --stdout > eigen.patch`, where `<tag>` is the tag, branch or commit from step 1