RFR: Add start on a section about logging

[Ludvig Janiuk]

It's hard to find information on how one should write logging code in Hotspot. This PR is only a first attempt at pointing the reader in the right direction, but a lot could be added in the future:
 * In which contexts can one not use unified logging?
 * How much should one log?
 * What other logging strategies are there?

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Commit messages:
 - fix trailing whitespace
 - fix
 - Add start on a section about logging

Changes: https://git.openjdk.java.net/guide/pull/70/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=70&range=00
  Stats: 34 lines in 1 file changed: 34 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/guide/pull/70.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/70/head:pull/70

PR: https://git.openjdk.java.net/guide/pull/70