Add description, keywords and licenses to sample buildpacks

[dfreilich]

Add Implementation of buildpacks/rfcs#127

buildpacks/pack#1022 adds the functionality to pack to parse the description, keywords and licenses keys in a buildpack.toml. They should be added to some of the samples, in order to demonstrate how people can do them.

e.g.

[buildpack]
id = "samples/hello-world"
version = "0.0.1"
name = "Hello World Buildpack"
homepage = "https://github.com/buildpacks/samples/tree/main/buildpacks/hello-world"
descripton = "some-description"
keywords = ["something", "something-b"]
[[buildpack.licenses]]
type="MIT"
uri="https://example.com/license"

[[buildpack.licenses]]
type="MIT2"
uri="https://example.com/license"