DOC: Ensure cheatsheets directory exists

Author: trallard

.github/workflows/ci.yml

@@ -148,7 +148,9 @@ jobs:
       run: mv doc/build/html web/build/docs
 
     - name: Copy cheatsheets into site directory
-      run: cp doc/cheatsheet/Pandas_Cheat_Sheet* web/build/docs/cheatsheet
+      run: |
+        mkdir -p web/build/docs/cheatsheets
+        cp doc/cheatsheet/Pandas_Cheat_Sheet* web/build/docs/cheatsheets
 
     - name: Save website as an artifact
       uses: actions/upload-artifact@v2