Add short description on what 'tech stack' means

[tmattsso]

Users that are not familiar with the Java ecosystem do not know what the different tech stack options mean. We don't need to explain them in detail, but only adding a short description to the filed will help:

Please choose what backend framework you would like, or plain Java for no framework. We recommend new users choose Spring.

Something like that gives the user some idea of what they are choosing, and giving them an OK for being noobs and not knowing.