Document Teams setup in Mattermost's generated README

Team Edition includes multiple Teams natively (no Enterprise license
needed), but nothing in the generated README said so or explained how
to create one. Added a Teams section covering creation, adding
members, and multi-team membership, plus a one-line pointer in the
install summary.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NQkdAn3iG5A4WoqU9FHMaN

services/mattermost.sh

@@ -379,7 +379,31 @@ Team messaging with voice/video calls. PostgreSQL backend + coturn TURN relay.
 
 ## Access
 - URL: $SITE_URL (or http://localhost:8065)
-- First run: create admin account at the URL above
+- First run: create admin account at the URL above — this account becomes
+  System Admin automatically.
+
+## Teams
+Team Edition (the free edition this installer uses) includes multiple Teams
+natively — separate spaces (their own channels, their own members) on the
+same server, same database, same login. No Enterprise license needed; this
+is the resource-efficient alternative to running a second Mattermost
+instance for a second group.
+
+Create one:
+- Click the **+** at the bottom of the team sidebar (the narrow column on
+  the far left) → **Create a new team**, or
+- System Console → User Management → Teams → **Create Team**
+
+Add people to a team:
+- Team name (top-left) → **Invite People** → share the invite link, or send
+  email invites (requires SMTP — System Console → Environment → SMTP), or
+- System Console → User Management → Teams → the team → **Add Members**
+  (adds existing server accounts directly, no invite flow)
+
+Users can belong to more than one team and switch between them via the team
+sidebar icons. By default any user can create a team — restrict that at
+System Console → User Management → Permissions if you only want admins
+creating them.
 
 ## Voice/Video Calls (Calls plugin)
 Port 8443/udp must be open on your router/firewall.
@@ -413,6 +437,8 @@ MD
     echo ""
     echo "  Access at:  $SITE_URL"
     echo "  First run:  open the URL above and create your admin account."
+    echo "  Teams:      team sidebar '+' → Create a new team (see README.md — no"
+    echo "              Enterprise license needed, Team Edition includes this)."
     echo "  Calls plugin: System Console → Plugins → Calls to configure coturn."
     echo "    TURN URI:    turn:${SITE_DOMAIN:-YOUR_IP}:3479?transport=udp"
     echo "    Auth secret: see COTURN_SECRET in $DIR/.env"