virsh-help: add page (#5910)

pages/common/virsh-help.md

@@ -0,0 +1,21 @@
+# virsh-help
+
+> Display information about `virsh` commands or command groups.
+> See also: `virsh`.
+> More information: <https://manned.org/virsh>.
+
+- List the `virsh` commands grouped into related categories:
+
+`virsh help`
+
+- List the command categories:
+
+`virsh help | grep "keyword"`
+
+- List the commands in a category:
+
+`virsh help {{category_keyword}}`
+
+- Show help for a command:
+
+`virsh help {{command}}`