Mention that search is prefix-based

This explains the difference that it makes as opposed to substring-based
search.

docs/how-to-guides/new-user-guides/add-users-to-projects.md

@@ -32,7 +32,8 @@ Following project creation, you can add users as project members so that they ca
 1. Search for the user or group that you want to add to the project. Note that:
   * At least 2 characters must be typed in the search box for results to appear
   * Users can be searched based on their username or display name
-  * Search is case-sensitive
+  * Search is prefix-based (eg. a user named `Stan Dard` will appear when searching for `Sta`, but not when searching
+    for `Dar`) and case-sensitive
 
     If external authentication is configured:
 

docs/how-to-guides/new-user-guides/manage-clusters/access-clusters/add-users-to-clusters.md

@@ -34,7 +34,8 @@ Cluster administrators can edit the membership for a cluster, controlling which
 1. Search for the user or group that you want to add to the cluster. Note that:
   * At least 2 characters must be typed in the search box for results to appear
   * Users can be searched based on their username or display name
-  * Search is case-sensitive
+  * Search is prefix-based (eg. a user named `Stan Dard` will appear when searching for `Sta`, but not when searching
+    for `Dar`) and case-sensitive
 
     If external authentication is configured:
 

docs/how-to-guides/new-user-guides/manage-clusters/projects-and-namespaces.md

@@ -172,7 +172,8 @@ To add members:
   * You can only search for groups if external authentication is enabled
   * At least 2 characters must be typed in the search box for results to appear
   * Users can be searched based on their username or display name
-  * Search is case-sensitive
+  * Search is prefix-based (eg. a user named `Stan Dard` will appear when searching for `Sta`, but not when searching
+    for `Dar`) and case-sensitive
 1. In the **Project Permissions** section, choose a role. For more information, refer to the [documentation on project roles.](../authentication-permissions-and-global-configuration/manage-role-based-access-control-rbac/cluster-and-project-roles.md)
 
 ### 4. Optional: Add Resource Quotas