building-introduction: Fix some nits

See #565

Author: bbhtt

docs/building-introduction.rst

@@ -19,9 +19,9 @@ allows you to take the source files for an application and build it into a
 Flatpak application. It also allows multiple other dependencies to be built
 at the same time, which get bundled into the build.
 
-It is packaged by several distributions and there is a
+It is packaged by several distributions and there is also a
 `Flatpak package <https://flathub.org/apps/org.flatpak.Builder>`_ called
-``org.flatpak.Builder`` available for it too on Flathub.
+``org.flatpak.Builder`` available for it on Flathub.
 
 The input to ``flatpak-builder`` is a manifest file. This specifies the
 parameters for the application that will be built, such as its name and