Improve extractor command example in README.md

Author: data-douser

README.md

@@ -1,5 +1,7 @@
 # CodeQL: SAP JavaScript frameworks
 
+[cloud-cap-samples]: https://github.com/SAP-samples/cloud-cap-samples
+
 This repository contains [CodeQL](https://codeql.github.com/) models and queries for SAP JavaScript frameworks:
 
 - [CAP](javascript/frameworks/cap) [https://cap.cloud.sap](https://cap.cloud.sap/)
@@ -109,14 +111,28 @@ codeql database analyze <DB_NAME> --format=sarif-latest --output=<OUTPUT_FILE> \
 
 The following example invocation of `codeql database create` includes the `--command` option to invoke the CDS extractor as an extension of the `javascript` extractor, which is used by `codeql` to create the database. The `pre-finalize.sh` script is a minimal wrapper around the `codeql database index-files` command, which we expect to run the `extractors/cds/tools/index-files.js` script to index the JSON files pre-generated by the CDS extractor.
 
+The below example assumes that:
+
+- The [`SAP-samples/cloud-cap-samples`][cloud-cap-samples] repository has been cloned to a sibling directory of the one containing the this repository.
+- The [`SAP-samples/cloud-cap-samples`][cloud-cap-samples] repository is intended as the source code root (i.e. target project) for the database.
+- The database directory (e.g., `~/codeql-home/databases/cloud-cap-samples-real`) is either absent or empty.
+
 ```shell
-codeql database create \
-  --search-path ./extractors/ \
-  --language javascript \
-  --command "./extractors/javascript/tools/pre-finalize.sh" \
-  ~/codeql-home/databases/cloud-cap-samples-real
+_d="$(pwd)" && codeql database create \
+  --command="${_d}/extractors/javascript/tools/pre-finalize.sh" \
+  --language="javascript" \
+  --search-path="${_d}/extractors/" \
+  --source-root="${_d}/../cloud-cap-samples/" \
+  -- ~/codeql-home/databases/cloud-cap-samples-real
 ```
 
+NOTES:
+
+- The `--source-root` option must be adjusted to match the actual location of the target project (e.g., GitHub repository).
+- The database directory path (last argument) must be adjusted to match the desired location of the created database.
+- Running the above command multiple times with the same database directory will result in an error. The `--overwrite` command-line option can be used to avoid this error.
+- See `codeql database create -h -v` for verbose command help.
+
 ## License
 
 This project is licensed under the terms of the MIT open source license. Please refer to [MIT](LICENSE.txt) for the full terms.