Update README.md to update submodules when cloning the repository

[notraceofsense]

Updated git clone command examples to use --recurse-submodules

Mark the type contribution you are making:

• [x] Documentation change (no change to underlying code, but makes documentation a little simpler)

Description

I replaced the three separate git clone, cd Delta, and git submodule commands with a --recurse-submodules option, which is equivalent. This removes a potential hiccup in getting ready to work with the codebase of forgetting to initialize the submodules.

Testing

Ran the command in question and it did the same thing as the current set of commands.

Checklist

General (All PRs)

• [N/A] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [N/A] I have commented my code, particularly in hard-to-understand areas
• [N/A] My changes generate no new warnings
• [N/A] I've tested my changes with different device + OS version configurations

[grndng]

Before merging this I'd recommend to merge https://github.com/rileytestut/Delta/pull/145 because the submodules can not be accessed with SSH and @katagaki has modified the .gitmodules file already.

[jaimegarjr]

Thanks for working on this! This would have been useful to know when setting up my local dev env.