Update docs/source/config_files.rst

Co-Authored-By: davidanthoff <anthoff@berkeley.edu>

docs/source/config_files.rst

@@ -89,7 +89,7 @@ of the Julia packages that are installed.
 
 A ``REQUIRE`` file can specify both the version of Julia to be used and
 which Julia packages should be used. The use of ``REQUIRE`` is only
-recommended for pre 1.0 Julia versions, the recommended way of installing
+recommended for pre 1.0 Julia versions. The recommended way of installing
 a Julia environment that uses Julia 1.0 or newer is to use a ``Project.toml``
 file. If both a ``REQUIRE`` and a ``Project.toml`` file are detected,
 the ``REQUIRE`` file is ignored. To see an example of a Julia repository