DOCSP-36043 adds mongod --dbpath --logpath example to install docs (#6117)

* adds mongod --dbpath --logpath example to install docs

* adds missing --fork

Author: jmd-mongo

source/tutorial/install-mongodb-on-os-x.txt

@@ -204,8 +204,8 @@ MongoDB as a macOS service, as doing so sets the correct system
 
      brew services stop mongodb-community@{+version+}
 
-- To run MongoDB (i.e. the :binary:`~bin.mongod` process) **manually
-  as a background process**, run:
+- To run :binary:`~bin.mongod` **manually as a background process**
+  using a config file, run:
 
   - For macOS running Intel processors:
 
@@ -220,6 +220,14 @@ MongoDB as a macOS service, as doing so sets the correct system
 
        mongod --config /opt/homebrew/etc/mongod.conf --fork
 
+- To run ``mongod`` **manually as a background process** specifying 
+  :option:`--dbpath <mongod --dbpath>` and :option:`--logpath
+  <mongod --logpath>` on the command line, run:
+
+  .. code-block:: bash
+
+     mongod --dbpath /path/to/dbdir --logpath /path/to/mongodb.log --fork
+
   To stop a :binary:`~bin.mongod` running as a background process,
   connect to the :binary:`~bin.mongod` using :mongosh:`mongosh </>`,
   and issue the :dbcommand:`shutdown` command as needed.