Fix trivial doc typo.

Author: anntzer

doc/command_ref.rst

@@ -978,7 +978,7 @@ resulting packages matching the specification. All packages are considered if no
     Limit the resulting set to packages that provide an upgrade for some already installed package.
 
 ``--userinstalled``
-    Limit the resulting set to packages instaled by user. The :ref:`exclude <exclude-label>` option
+    Limit the resulting set to packages installed by user. The :ref:`exclude <exclude-label>` option
     in configuration file (.conf) might influence the result, but if the command line option  \-\
     :ref:`-disableexcludes <disableexcludes-label>` is used, it ensures that all installed packages will be listed.