Explain how to compile the TypeScript code sample

[PierreFritsch]

• Clarify how to implement the recommendation given on the capire page Using TypeScript:

  For productive usage always precompile TypeScript code to JavaScript due to performance reasons and use the cds binary.

• Add tsconfig.json in order to ensure that the generated JavaScript files can be understood by CAP and prevent error messages like:

  Service "say" has no handler for "hello".

[renejeglinsky]

PING :) @danjoa @chgeo

[PierreFritsch]

Originally proposed to:

• Extract the Hello World! TypeScript code sample to a dedicated folder in order to avoid polluting the Hello World! JavaScript code sample.

but the CAP team decided not have a separate variant of the hello package (communicated internally by @chgeo), so moved back the missing TypeScript pieces to this folder.

[PierreFritsch]

Internal ticket is cap/issues#9166. This PR was adapted with the requested changes.