RFR: Added git in backout description

[Jesper Wilhelmsson]

What the title say.

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Commit messages:
 - Added git in backout description

Changes: https://git.openjdk.java.net/guide/pull/61/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=61&range=00
  Stats: 48 lines in 1 file changed: 46 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/guide/pull/61.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/61/head:pull/61

PR: https://git.openjdk.java.net/guide/pull/61