Improve documentation of delete-all target

Explain that delete-all actually leaves behind some resources
that were created manually.

Bug: Issue 13059
Change-Id: Iedfd7ffa4092614532d5c71f27c86e90195aea4b
diff --git a/dual-master/README.md b/dual-master/README.md
index abd0366..48b7c1e 100644
--- a/dual-master/README.md
+++ b/dual-master/README.md
@@ -118,6 +118,11 @@
 make delete-all
 ```
 
+Note that this will *not* delete:
+* Secrets stored in Secret Manager
+* SSL certificates
+* ECR repositories
+
 ### Access your Gerrit instances
 
 Get the URL of your Gerrit master instances this way:
diff --git a/master-slave/README.md b/master-slave/README.md
index 99297bf..92428f0 100644
--- a/master-slave/README.md
+++ b/master-slave/README.md
@@ -115,6 +115,12 @@
 make delete-all
 ```
 
+
+Note that this will *not* delete:
+* Secrets stored in Secret Manager
+* SSL certificates
+* ECR repositories
+
 ### Access your Gerrit instances
 
 Get the URL of your Gerrit master instance this way:
diff --git a/single-master/README.md b/single-master/README.md
index 80cfcd3..7063296 100644
--- a/single-master/README.md
+++ b/single-master/README.md
@@ -110,6 +110,11 @@
 make delete-all
 ```
 
+Note that this will *not* delete:
+* Secrets stored in Secret Manager
+* SSL certificates
+* ECR repositories
+
 ### Access your Gerrit
 
 You Gerrit instance will be available at this URL: `http://<HOSTED_ZONE_NAME>.<SUBDOMAIN>`.