[clangd][vscode] update the development doc.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@371986 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/clangd/clients/clangd-vscode/DEVELOPING.md b/clangd/clients/clangd-vscode/DEVELOPING.md
index 92aad52..a15d050 100644
--- a/clangd/clients/clangd-vscode/DEVELOPING.md
+++ b/clangd/clients/clangd-vscode/DEVELOPING.md
@@ -48,6 +48,6 @@
   # For the first time, you need to login in the account. vsce will ask you for
     the Personal Access Token, and remember it for future commands.
   $ vsce login llvm-vs-code-extensions
-  $ vsce publish
+  # Make sure the screenshots in the readme are rendered in VSCode marketplace.
+  $ vsce publish --baseImagesUrl https://raw.githubusercontent.com/llvm/llvm-project/master/clang-tools-extra/clangd/clients/clangd-vscode/
 ```
-