cmd ref: improve note about verify option and add it to remote add-…

…> GDrive

per #937 (comment)

public/static/docs/command-reference/remote/add.md

@@ -240,6 +240,12 @@ drive is opened. For example, for the URL
 $ dvc remote add myremote gdrive://0AIac4JZqHhKmUk9PDA/my-dvc-root
 ```
 
+Note that GDrive remotes are not "trusted" by default. This means that the
+[`verify`](`/doc/command-reference/remote/modify#available-settings-for-all-remotes`)
+option is enabled on this type of storage, so DVC recalculates the checksums of
+files upon download (e.g. `dvc pull`), to make sure that these haven't been
+modified.
+
 </details>
 
 <details>

public/static/docs/command-reference/remote/modify.md

@@ -63,10 +63,12 @@ manual editing could be used to change the configuration.
 
 The following options are available for all remote types:
 
-- `verify` - upon downloading cache files (`dvc pull`, `dvc fetch`) DVC will
-  recalculate downloaded file checksums to make sure that these are not
-  corrupted or modified during download. It may slow down the aforementioned
-  commands.
+- `verify` - upon downloading <abbr>cache</abbr> files (`dvc pull`, `dvc fetch`)
+  DVC will recalculate the checksums of files upon download (e.g. `dvc pull`) to
+  make sure that these haven't been modified, or corrupted during download. It
+  may slow down the aforementioned commands.
+
+  > Note that this option is enabled on **Google Drive** remotes by default.
 
   ```dvc
   $ dvc remote modify myremote verify true