change heading style in preprocessor documentation

wnienhaus · wnienhaus · commit e3bd8bf7e403 · 2021-10-17T18:25:43.000+03:00
Differentiate between a main heading and subsection headings.
This mirrors the change also done in the main README.
diff --git a/docs/preprocess.rst b/docs/preprocess.rst
@@ -1,5 +1,6 @@
+=====================
 Preprocessor
----------------------
+=====================
 
 py-esp32-ulp contains a small preprocessor, which aims to fulfill one goal:
 facilitate assembling of ULP code from Espressif and other open-source
