[mcp2515] add section about limitations (#5319)

Author: patagonaa

content/components/canbus/esp32_can.md

@@ -7,6 +7,8 @@ params:
     image: canbus.svg
 ---
 
+{{< anchor "esp32-can" >}}
+
 The ESP32 has an integrated CAN controller and therefore doesn't necessarily need an external controller.
 You only need to specify the RX and TX pins. Any GPIO will work.
 

content/components/canbus/mcp2515.md

@@ -33,6 +33,14 @@ canbus:
             brightness: !lambda "return (x.size() > 0) ? (float) x[0]/255 : 0;"
 ```
 
+{{< note >}}
+The MCP2515 only provides two receive buffers which are read once per loop cycle.  
+This means, if more than two CAN frames arrive within a loop cycle (typically 16ms, possibly longer), frames are dropped.
+
+This limitation makes the MCP2515 unsuitable for moderate- to high-speed CAN buses, especially automotive ones.  
+Use the [esp32_can](#esp32-can) component where possible.
+{{< /note >}}
+
 ## Configuration variables
 
 - **cs_pin** (**Required**, [Pin Schema](#config-pin_schema)): Is used to signal to a SPI device when it should