doc(spi): update README.md

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

Author: fpistm

libraries/SPI/README.md

@@ -42,7 +42,8 @@ void setup() {
 #### Change default `SPI` instance pins
 It is also possible to change the default pins used by the `SPI` instance using above API:
 
-[[/img/Warning-icon.png|alt="Warning"]] **Have to be called before `begin()`.**
+> [!WARNING]
+> **Have to be called before `begin()`.**
 
 * `void setMISO(uint32_t miso)`
 * `void setMOSI(uint32_t mosi)`
@@ -53,7 +54,8 @@ It is also possible to change the default pins used by the `SPI` instance using
 * `void setSCLK(PinName sclk)`
 * `void setSSEL(PinName ssel)`
 
-**_Note 1_** Using `setSSEL()` allows to enable hardware CS pin management linked to the SPI peripheral.
+> [!NOTE]
+> Using `setSSEL()` allows to enable hardware CS pin management linked to the SPI peripheral.
 
 ##### Example:
 ```C++