sqlite: Clarify README roll-dep command.

Change-Id: I57fc90c6261903f3ad5afe8833c226b8bbfde3e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153945
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Chris Mumford <cmumford@google.com>
Cr-Commit-Position: refs/heads/master@{#759897}

third_party/sqlite/README.md

@@ -76,7 +76,7 @@ tools and is not distributed.
 
     1. Roll the `chromium/src/DEPS` file to reference that new commit ID.
         ```sh
-        roll-dep src/third_party/sqlite/src
+        roll-dep src/third_party/sqlite/src --roll-to <git hash of merged CL>
         ```
     2. Update the version in //third_party/sqlite/README.chromium. Append the
        commit created by roll-dep above.
@@ -139,7 +139,7 @@ following:
     reference that new commit ID.
 
     ```sh
-    roll-dep src/third_party/sqlite/src
+    roll-dep src/third_party/sqlite/src --roll-to <git hash of merged CL>
     ```
 
 # Running Tests