Replace -S with -P in npm install instruction

[asudoh]

When I follow the instructions in the top-level README file to install the component library:

npm install -S carbon-web-components carbon-components

I find that it leads to a peer dependency conflict:

✗ npm install --save carbon-web-components carbon-components
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: ft-widget@1.0.0
npm ERR! Found: carbon-components@10.34.0
npm ERR! node_modules/carbon-components
npm ERR!   carbon-components@"^10.34.0" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer carbon-components@"~10.32.0" from carbon-web-components@1.13.1
npm ERR! node_modules/carbon-web-components
npm ERR!   carbon-web-components@"*" from the root project

Looking at the change history of the project's package.json file, I see that the version of carbon-components library dependency is locked down (using the tilde version specifier) and is periodically bumped up. Presumably somebody is carefully testing that the carbon-web-components library is in fact compatible with the newer version of the carbon-components library. But is it truly necessary to lock down versions that tightly? If it is, people should be told to specify the versions explicitly in the npm install comand:

npm install --save carbon-components@10.32.0 carbon-web-components@1.13.1

That works, but specifying versions in this way is not something that I can recall seeing before. It seems like something outside of best practices.

Also: The use of the "-S" option in the README's npm command example no longer works. Would be good to change:

npm install -S carbon-web-components carbon-components lit-html lit-element

to:

npm install --save carbon-web-components carbon-components lit-html lit-element

Originally posted by @TrentBrown in #557 (comment)