RFR: 8320526: Use title case in building.md

Tue Nov 21 16:04:38 UTC 2023

We should use title case consistently in building.md.

I thought I was done with fixing up the build README, but then I noticed this and I couldn't unsee it...

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Commit messages:
 - 8320526: Use title case in building.md

Changes: https://git.openjdk.org/jdk/pull/16765/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16765&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320526
  Stats: 29 lines in 2 files changed: 0 ins; 0 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/16765.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16765/head:pull/16765

PR: https://git.openjdk.org/jdk/pull/16765