message: Add flow diagram headers to sensor file
diff: @@ -23,6 +23,8 @@ buttons, etc.
  matching Id on successful request.
  * Error message on value or message error.
  +**Flow Diagram:**
  +
  <mermaid>
  sequenceDiagram
  Client->>Server: BatteryLevelCmd Id=1
  @@ -57,8 +59,9 @@ device, as requested by [BatteryLevelCmd](sensors.html#batterylevelcmd).
  **Expected Response:**
  -* BatteryLevelReading message with matching Id on successful request.
  -* Error message on value or message error.
  +* None. Server-to-Client message only.
  +
  +**Flow Diagram:**
  <mermaid>
  sequenceDiagram
  @@ -97,6 +100,8 @@ sequenceDiagram
  matching Id on successful request.
  * Error message on value or message error.
  +**Flow Diagram:**
  +
  <mermaid>
  sequenceDiagram
  Client->>Server: RSSILevelCmd Id=1
  @@ -131,8 +136,9 @@ device, as requested by [RSSILevelCmd](sensors.html#rssilevelcmd).
  **Expected Response:**
  -* RSSILevelReading message with matching Id on successful request.
  -* Error message on value or message error.
  +* None. Server-to-Client message only.
  +
  +**Flow Diagram:**
  <mermaid>
  sequenceDiagram
  