RFR: Section on sponsoring [v10]

[Jesper Wilhelmsson]

> Copied and updated the text from the old sponsoring page: https://openjdk.org/sponsor/
> The purpose is to have the sponsor link on the OpenJDK page lead here instead.
> 
> Also updated the contributing section with some parts taken from the old contributing page: https://openjdk.org/contribute/
> Again, the intention is to change the link on the OpenJDK page to lead here.

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

 - More fixes after review
 - Fixes after review

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

Changes:
  - all: https://git.openjdk.org/guide/pull/97/files
  - new: https://git.openjdk.org/guide/pull/97/files/e528eda8..9f83b708

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=guide&pr=97&range=09
 - incr: https://webrevs.openjdk.org/?repo=guide&pr=97&range=08-09

  Stats: 11 lines in 1 file changed: 4 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/guide/pull/97.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/97/head:pull/97

PR: https://git.openjdk.org/guide/pull/97