FlatBuffers update: add docs for update script.

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/flatbuffers/README.md

@@ -6,6 +6,9 @@ to avoid conflicts with FlatBuffers generated Java code from users of this libra
 Current version: see `Constants.java`.
 
 Copy a different version using the script in `scripts\update-flatbuffers.sh`.
+It expects FlatBuffers source files in the `../flatbuffers` directory (e.g. check out
+the desired FlatBuffers tag from https://github.com/google/flatbuffers next to this repo).
+The Java library is expected in `objectbox-java`, e.g. run the script from the root of this repo.
 
 ## Licensing
 

scripts/update-flatbuffers.sh

@@ -1,6 +1,9 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+# Expects FlatBuffers source files in the `../flatbuffers` directory,
+# the Java library in `objectbox-java`, e.g. run this from the root of this repo.
+
 script_dir=$(dirname "$(readlink -f "$0")")
 cd "${script_dir}/.." # move to project root dir or exit on failure
 echo "Running in directory: $(pwd)"