docs: add apt clarification to faq c lib section

Author: rokroskar

docs/faq.rst

@@ -37,13 +37,13 @@ which details your dependencies. See our guide on :ref:`guides/reproducible-buil
 You can also set your project documentation to install your project itself
 as a dependency.
 
-Additionally, your build may depend on extensions that require additional
-system packages to be installed. If you are using a :ref:`configuration
-file <config-file>` you can add libraries to the Ubuntu-based builder with
-``apt``.
+Your build may depend on extensions that require additional system packages to
+be installed. If you are using a :doc:`Configuration File <config-file/v2>` you
+can :ref:`add libraries with apt <config-file/v2:build.apt_packages>` to the
+Ubuntu-based builder .
 
-If your project or its dependencies rely on C libraries,
-see :ref:`faq:I get import errors on libraries that depend on C modules`.
+If your project or its dependencies rely on C libraries that cannot be installed
+this way, see :ref:`faq:I get import errors on libraries that depend on C modules`.
 
 
 My project requires some additional settings
@@ -65,12 +65,15 @@ I get import errors on libraries that depend on C modules
 
    Another use case for this is when you have a module with a C extension.
 
-This happens because our build system doesn't have the dependencies for building your project.
-This happens with things like ``libevent``, ``mysql``, and other Python packages that depend on C libraries.
-We can't support installing random C binaries on our system, so there is another way to fix these imports.
+This happens because the build system does not have the dependencies for
+building your project, such as C libraries needed by some Python packages (e.g.
+``libevent`` or ``mysql``). For libraries that cannot be :ref:`installed via apt
+<config-file/v2:build.apt_packages>` in the builder there is another way to
+successfully build the documentation despite missing dependencies.
 
-With Sphinx you can use the built-in `autodoc_mock_imports`_ for mocking.
-If such libraries are installed via ``setup.py``, you also will need to remove all the C-dependent libraries from your ``install_requires`` in the RTD environment.
+With Sphinx you can use the built-in `autodoc_mock_imports`_ for mocking. If
+such libraries are installed via ``setup.py``, you also will need to remove all
+the C-dependent libraries from your ``install_requires`` in the RTD environment.
 
 .. _autodoc_mock_imports: http://www.sphinx-doc.org/en/master/usage/extensions/autodoc.html#confval-autodoc_mock_imports