Clarifying test process

This test process should only be used by core team, since it references Core team site,

doc/developer/tests/test-attachments.md

@@ -1,5 +1,5 @@
 # Testing Files and Attachments
-This test contains instructions to manual test common attachment types. All files for testing are stored in the [mm_file_testing](https://www.dropbox.com/sh/i7ft8is5hbhk8ii/AAAyM-WG-X2jiQOgg6-E3MmLa?dl=0) dropbox folder. Follow these instructions:
+This test contains instructions for the core team to manually test common attachment types. All files for testing are stored in the [mm_file_testing](https://www.dropbox.com/sh/i7ft8is5hbhk8ii/AAAyM-WG-X2jiQOgg6-E3MmLa?dl=0) dropbox folder. Follow these instructions:
 
 1. Download the entire [mm_file_testing](https://www.dropbox.com/sh/i7ft8is5hbhk8ii/AAAyM-WG-X2jiQOgg6-E3MmLa?dl=0) folder. 
 2. Drag and drop each file type into Mattermost to upload it.