docs(filemanager): add note about permission issues

Author: mmalenic

lib/workload/stateless/filemanager/.gitignore

@@ -2,4 +2,4 @@ target/
 *.swp
 /volume/
 .build
-target-cdk-docker-bundling/
+target-cdk-docker-bundling/

lib/workload/stateless/filemanager/deploy/README.md

@@ -21,3 +21,11 @@ The filemanager expects a dedicated database within the shared database cluster,
 Initially, the filemanager-migrate-lambda function is deployed to perform database table migrations using the
 cdk_resource_invoke.ts construct. Then, the other Lambda functions are deployed normally within the filemanager
 construct.
+
+### Building
+
+Note, the `RustFunction` compiles code using `cargo-lambda` running inside a Docker container, and produces a Lambda
+function which runs natively on AWS (i.e. not a dockerized Lambda function). This makes it simpler for consumers of
+the Filemanager CDK to build the project. There is a small downside in that the compiled code is stored under a 
+`target-cdk-docker-bundling` directory which is owned by Docker, so there may be some permission issues if trying to 
+clean this directory.