README needs clarifications

[mernst]

In the README file, https://github.com/actions/setup-java#v2-vs-v1 discusses V1 vs V2. It would be good to also mention v3, which is used later in the README. It also might be good to move that section later in the README.

The section on Supported version syntax suggests that only 8, 11, 16, and 17 are permitted. If those are examples rather than an exhaustive list, please state that explicitly.

Thanks.

[dmitry-shibanov]

Hello @mernst. Thank you for your report. I'm not sure that it is necessary because the only breaking change from v2 to v3 was switching node12 to node16.

[mernst]

I think the current wording is fine for someone who is already familiar with the setup-java action (like you! and like me, now). However, the README is especially useful for someone who doesn't already know the details: someone who needs to be taught how setup-java works rather than merely reminded of it.

Regarding my first suggestion: The beginning of the README suggests that the only two versions that exist are V1 and V2. I found this confusing (I went to use V2, which immediately failed because I needed V3). I think it would be helpful (and not overly verbose or distracting) to mention that V3 also exists.

Similarly for my second suggestion, about supported version syntax.

[dmitry-shibanov]

Thank you for your suggestion @mernst. We'll take a look on it.