added two mongo examples

mongo/add-field-with-default-value.js

@@ -0,0 +1,5 @@
+db.getCollection('myCollection').update(
+    {$or:[{"name":null},{"name":{$exists:false}}]},
+    {$set:{"name":"default, value"}}, 
+    {multi:true}
+);

mongo/collectionNames-and-count.js

@@ -0,0 +1,18 @@
+var result = [];
+db.getCollectionInfos().forEach(function(collection) {
+    var collectionResult = {name: collection.name, count: db[collection.name].count()}
+    result.push(collectionResult);
+});
+printjson(result); 
+
+// resulting in:
+// [
+// 	{
+// 		"name" : "test",
+// 		"count" : 1
+// 	},
+// 	{
+// 		"name" : "test2",
+// 		"count" : 3
+// 	}
+// ]