Docs: Created the Wasmtime Markdown Parser Example (#3193)

* Finished the Markdown Parser Example for Wasmtime

* Made requested changes

* Tiny change to explanation of `--dir` CLI arg

* Add `bash` annotations to shell script code blocks

* Trying to fix the markdown example bug

* Figured out rustdoc, and what needed to be done

* Made requested changes

Co-authored-by: Till Schneidereit <till@tillschneidereit.net>

Cargo.toml

@@ -79,7 +79,10 @@ members = [
   "examples/tokio/wasm",
   "fuzz",
 ]
-exclude = ['crates/wasi-common/WASI/tools/witx-cli']
+exclude = [
+  'crates/wasi-common/WASI/tools/witx-cli', 
+  'docs/rust_wasi_markdown_parser'
+  ]
 
 [features]
 default = ["jitdump", "wasmtime/wat", "wasmtime/parallel-compilation", "wasi-nn"]