Fix local path insertion of package, fix more docs

Add back git installation docs, we'll discuss this separately.

docs/installing.rst

@@ -27,3 +27,15 @@ In your ``conf.py`` file:
     strings in your translated output. If these strings are not translated in
     your output, either we lack the localized strings for your locale, or you
     are using an old version of the theme.
+
+Via Git or Download
+===================
+
+Symlink or subtree the ``sphinx_rtd_theme/sphinx_rtd_theme`` repository into your documentation at
+``docs/_themes/sphinx_rtd_theme`` then add the following two settings to your Sphinx
+``conf.py`` file:
+
+.. code:: python
+
+    html_theme = "sphinx_rtd_theme"
+    html_theme_path = ["_themes", ]