docs: add verified group creation example

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/user-management.md

@@ -98,6 +98,20 @@ kanidm group get <group-name>
 kanidm group list-members <group-name>
 ```
 
+### Example: Full Group Creation
+
+```bash
+kanidm group create testgroup
+kanidm group posix set testgroup --gidnumber 68010
+kanidm group add-members testgroup testuser
+kanidm group get testgroup
+```
+
+After creation, verify on a client host:
+```bash
+getent group testgroup
+```
+
 ### Current Groups
 
 | Group | GID | Purpose |