RFR: Added section for newcomers [v2]

[Jesper Wilhelmsson]

> Added a section to the introduction to set the expectations for new developers in the OpenJDK.
> 
> I also moved the mail list section up since it's also relevant in this context and should (imho) be the first thing to learn about when thinking about joining the community.

Jesper Wilhelmsson has updated the pull request incrementally with two additional commits since the last revision:

 - OCA
   
   Co-authored-by: Magnus Ihse Bursie <mag at icus.se>
 - Member of list
   
   Co-authored-by: Magnus Ihse Bursie <mag at icus.se>

-------------

Changes:
  - all: https://git.openjdk.java.net/guide/pull/38/files
  - new: https://git.openjdk.java.net/guide/pull/38/files/9a5a6a0c..f4dba31b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=guide&pr=38&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=guide&pr=38&range=00-01

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/guide/pull/38.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/38/head:pull/38

PR: https://git.openjdk.java.net/guide/pull/38