adding missing step of dependencies installation (#5492)

docs/examples-markdown.md

@@ -9,6 +9,12 @@ cargo new --bin rust_wasi_markdown_parser
 cd rust_wasi_markdown_parser
 ```
 
+Also, we need to add the `structopt` and `pulldown_cmark` crates to our project:
+
+```bash
+cargo add structopt pulldown_cmark
+```
+
 Then, we will open the `src/main.rs` and enter the following contents. Please see the comments to understand what our program will be doing.
 
 ## `src/main.rs`