Merge pull request #71 from firebase/rachelsaunders-bq-importscript

docs(firestore-bigquery-export): update import script instructions for npm info

Author: rachelsaunders

firestore-bigquery-export/guides/IMPORT_EXISTING_DOCUMENTS.md

@@ -1,27 +1,42 @@
+The `fs-bq-import-collection` script is for use with the official Firebase Extension [**Export Collections to BiqQuery**](https://github.com/firebase/extensions/tree/master/firestore-bigquery-export).
+
 ### Overview
 
-The import script (`fs-bq-import-collection`) can read all existing documents in a Cloud Firestore collection and insert them into the raw changelog table created by the Export Collections to BigQuery extension. The script adds a special changelog for each document with the operation of `IMPORT` and the timestamp of epoch. This ensures that any operation on an imported document supersedes the import record.
+The import script (`fs-bq-import-collection`) can read all existing documents in a Cloud Firestore collection and insert them into the raw changelog table created by the Export Collections to BigQuery extension. The import script adds a special changelog for each document with the operation of `IMPORT` and the timestamp of epoch. This ensures that any operation on an imported document supersedes the import record.
 
-You may pause and resume the script from the last batch at any point.
+You may pause and resume the import script from the last batch at any point.
 
 #### Important notes
 
-- Run the script over the entire collection **_after_** installing the Export Collections to BigQuery extension; otherwise the writes to your database during the import might not be exported to the dataset.
+- You must run the import script over the entire collection **_after_** installing the Export Collections to BigQuery extension; otherwise the writes to your database during the import might not be exported to the dataset.
+
 - The import script can take up to _O(collection size)_ time to finish. If your collection is large, you might want to consider [loading data from a Cloud Firestore export into BigQuery](https://cloud.google.com/bigquery/docs/loading-data-cloud-firestore).
-- You will see redundant rows in your raw changelog table:
 
-  - If document changes occur in the time between installing the extension and running this import script.
+- You will see redundant rows in your raw changelog table if either of the following happen:
+
+  - If document changes occur in the time between installing the extension and running the import script.
   - If you run the import script multiple times over the same collection.
 
-### Install and run the script
+### Run the script
 
-This import script uses several values from your installation of the extension:
+The import script uses several values from your installation of the extension:
 
 - `${PROJECT_ID}`: the project ID for the Firebase project in which you installed the extension
 - `${COLLECTION_PATH}`: the collection path that you specified during extension installation
 - `${DATASET_ID}`: the ID that you specified for your dataset during extension installation
 
-1.  Run `npx @firebaseextensions/fs-bq-import-collection`.
+Run the import script using [`npx` (the Node Package Runner)](https://www.npmjs.com/package/npx) via `npm` (the Node Package Manager).
+
+1.  Make sure that you've installed the required tools to run the import script:
+
+    - To access the `npm` command tools, you need to install [Node.js](https://www.nodejs.org/).
+    - If you use `npm` v5.1 or earlier, you need to explicitly install `npx`. Run `npm install --global npx`.
+
+1.  Run the import script via `npx` by running the following command:
+
+    ```
+    npx @firebaseextensions/fs-bq-import-collection
+    ```
 
 1.  When prompted, enter the Cloud Firestore collection path that you specified during extension installation, `${COLLECTION_PATH}`.