fix: underline too short

Author: henryiii

source/guides/packaging-binary-extensions.rst

@@ -233,14 +233,15 @@ Building binary extensions
 ==========================
 
 Building extensions for multiple platforms
--------------------------
-
-If you plan to distribute your extension, you should provide :term:`wheels <Wheel>` for all the
-platforms you intend to support. For most extensions, this is at least one
-package per Python version times the number of OS and architectures you support.
-These are usually built on continous integration (CI) systems. There are tools
-to help you build highly redistributable binaries from CI; these include
-:ref:`cibuildwheel` and :ref:`multibuild`.
+------------------------------------------
+
+If you plan to distribute your extension, you should provide
+:term:`wheels <Wheel>` for all the platforms you intend to support. For most
+extensions, this is at least one package per Python version times the number of
+OS and architectures you support.  These are usually built on continuous
+integration (CI) systems. There are tools to help you build highly
+redistributable binaries from CI; these include :ref:`cibuildwheel` and
+:ref:`multibuild`.
 
 
 Binary extensions for Windows