DOCSP-49213 documents db name requirement for excludeCollection options (#195)

* DOCSP-49213 documents db name requirement for excludeCollection commands

* Revises wording

* Fixes option name in excludeCollectionsWithPrefix

* revises wording

Author: jwilson-mdb

source/mongodump.txt

@@ -770,13 +770,21 @@ Options
 
    Excludes the specified collection from the ``mongodump`` output.
    To exclude multiple collections, specify the ``--excludeCollection`` multiple times.
+   
+   To use the ``--excludeCollection`` option, you must specify a database. You can specify
+   a database with the :option:`--db <mongodump --db>` option or in the
+   :option:`--uri <mongodump --uri>` connection string.
 
 .. option:: --excludeCollectionsWithPrefix=<string>
 
    Excludes all collections with a specified prefix from the ``mongodump``
    outputs. To specify multiple prefixes, specify the ``--excludeCollectionsWithPrefix`` multiple
    times.
 
+   To use the ``--excludeCollectionsWithPrefix`` option, you must specify a database. You can specify
+   a database with the :option:`--db <mongodump --db>` option or in the 
+   :option:`--uri <mongodump --uri>` connection string.
+
 .. option:: --numParallelCollections=<int>, -j=<int>
 
    *Default*: 4