corrected heading for SPI in README.rst

jandechent · web-flow · commit 76edc0e0e877 · 2020-01-10T14:58:00.000+01:00
the SPI heading was missing a ~, which read to it not showing as heading. This was corrected.
diff --git a/library/README.rst b/library/README.rst
@@ -130,7 +130,7 @@ When using PCM you cannot use digital audio devices which use I2S since
 I2S uses the PCM hardware, but you can use analog audio.
 
 SPI
-~~
+~~~
 
 When using SPI the ledstring is the only device which can be connected
 to the SPI bus. Both digital (I2S/PCM) and analog (PWM) audio can be
