RFR: Add start on a section about logging [v2]

[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?

Ludvig Janiuk has updated the pull request incrementally with one additional commit since the last revision:

  cleanup

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Changes:
  - all: https://git.openjdk.java.net/guide/pull/70/files
  - new: https://git.openjdk.java.net/guide/pull/70/files/140a4f93..0c5c333e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=guide&pr=70&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=guide&pr=70&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 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