DOCS-5715: Add warning on lock scope for dropIndexes shell helpers

Author: stennie

source/reference/method/db.collection.dropIndex.txt

@@ -32,6 +32,11 @@ Definition
    :method:`db.collection.dropIndex()` method, use the
    :method:`db.collection.getIndexes()` method.
 
+   .. warning::
+
+      This command obtains a write lock on the affected database and
+      will block other operations until it has completed.
+
 Example
 -------
 

source/reference/method/db.collection.dropIndexes.txt

@@ -15,3 +15,8 @@ db.collection.dropIndexes()
    Drops all indexes other than the required index on the ``_id``
    field. Only call :method:`~db.collection.dropIndexes()` as a method on a
    collection object.
+
+.. warning::
+
+    This command obtains a write lock on the affected database and
+    will block other operations until it has completed.