Say that files can live in Google Cloud Storage too

Three lines still told readers S3 was the only option, which stopped
being true and is the sort of thing somebody chooses a different product
over. The install guide's storage section now says what each backend is
for, that Test connection exists and is worth using before switching
uploads over, and — the part people actually get wrong — that choosing a
backend applies to new uploads and moves nothing that is already stored.

INSTALL.md

@@ -84,7 +84,7 @@ Two ways out, if nginx really is impossible on your hosting:
   rather than as a misconfiguration. This applies to any proxy in front of ProjectSend, not just
   this one: Nginx Proxy Manager, Traefik and a hand-written nginx vhost all ship the same default.
   ([#1664](https://github.com/projectsend/projectsend/issues/1664))
-- Store your files in S3-compatible object storage instead (see
+- Store your files in object storage instead — S3-compatible or Google Cloud Storage (see
   [Storing files somewhere other than this server](#storing-files-somewhere-other-than-this-server)).
   Files kept there are never on your server's disk, so downloads become a signed, expiring redirect
   to the storage provider and the web server is not involved at all. This is a genuine, supported
@@ -447,8 +447,20 @@ the worker afterwards.
 ### Storing files somewhere other than this server
 
 Out of the box, uploads live in `storage/app/files/` on this machine. You can point ProjectSend at
-S3-compatible object storage instead from **System → Settings → Storage** — useful when the files
-outgrow the server's disk.
+object storage instead from **System → Settings → Storage** — useful when the files outgrow the
+server's disk.
+
+Two backends are offered. **S3-compatible** covers AWS S3 and everything speaking that API: MinIO,
+Backblaze B2, Wasabi, DigitalOcean Spaces. Leave the endpoint blank for AWS itself, or set it to the
+service's own address and turn on path-style addressing, which most of them need. **Google Cloud
+Storage** takes a service account key with read and write access to the bucket, pasted in as the JSON
+file Google issues; it is stored encrypted and never shown again.
+
+Whichever you choose, use **Test connection** before switching uploads over — it checks the
+credentials actually reach the bucket, rather than leaving you to find out at the first upload.
+
+The setting applies to new uploads. Files already on local disk stay there and keep working, and
+there is no migration between backends.
 
 ### Making it faster
 

README.md

@@ -47,7 +47,7 @@ per-seat pricing. It runs on your server, and the files stay there.
 - 16 languages
 - A REST API with scoped tokens and generated OpenAPI docs
 - Privacy controls, including GDPR-grade account erasure with a grace period
-- Local disk or S3-compatible storage
+- Local disk, S3-compatible storage, or Google Cloud Storage
 
 ## Screenshots