docs: Fix Retail README headers (GoogleCloudPlatform#8967)

kweinmeister · web-flow · commit a85dbe9e078e · 2023-01-12T10:22:08.000-05:00
Missing spaces caused rendering like this:
```
#Retail Search Interactive Tutorials

##Run tutorials in Cloud Shell

To advance with the interactive tutorials, use Retail Search step-by-step manuals on the right side of
```
diff --git a/retail/interactive-tutorials/README.md b/retail/interactive-tutorials/README.md
@@ -1,6 +1,6 @@
-#Retail Search Interactive Tutorials
+# Retail Search Interactive Tutorials
 
-##Run tutorials in Cloud Shell
+## Run tutorials in Cloud Shell
 
 To advance with the interactive tutorials, use Retail Search step-by-step manuals on the right side of the Cloud Shell IDE: 
 ![Interactive tutorials](images/tutorial1.png)
@@ -185,4 +185,4 @@ python product/import_products_gcs.py
 Run the sample in a terminal with the following command:
 ```bash
 python search/search_with_boost_spec.py
-```
+```
