Improve performance of in-container commands with many write on disks

[toricls]

This PR improves container disk performance for the npx create-react-app command and fixes #2 by using in-container storage instead of mounted storage.

As excerpted from the updated README.md as follows, this PR includes a bash script to preserve files from remote container to user's host directory.

---

NOTE: You will find the boyaki directory in your remote container during the workshop (so as in the VSCode's explorer) but NOT in your host machine. This is a side-effect of the fix PR #3 (for the issue #2) to speed up the npx create-react-app command, thus you may lose your boyaki files once you stop the remote container. If you need to preserve and/or edit the files inside the boyaki folder outside of your remote container, you can use the bash script copy-boyaki-to-host.sh to copy those in-container files as a zip file boyaki.zip to your host machine's boyaki directory. Simply execute /workspaces/hostdir/copy-boyaki-to-host.sh /hostdir/copy-boyaki-to-host.sh inside your remote container and follow the guidance to run it.

[jaga810]

LTGM. Awesome work!
However it seems a bit confusing which to use workspaces or workspaces/hostdir.

I'd like to suggest to add below sentence at Usage section in READEME.md

• Your working directory is workspaces not workspaces/hostdir by default.

[toricls]

@jaga810 Thanks! That's a good point!

The only reason to mount the host directory was to make it available to copy the workshop output by a script execution within the working container, and there is no reason to keep the mount directory visible for users.

I'm thinking to change the directory structure as follows but can I have your thoughts on this? Is this still confusing for users?

/ <- container's root
...
├── hostdir <- The mounted host directory (moved out of 'workspaces')
...
└── workspaces <- Visible for users as their workspace as default, and will includes 'boyaki' folder during the workshop 

[jaga810]

@toricls It seems less confusing! I love the suggested change of directory structure.