[jdk16u] RFR: 8265531: doc/building.md should mention homebrew install freetype

[George Adams]

Backport of 8265531: doc/building.md should mention homebrew install freetype

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

Commit messages:
 - 8265531: doc/building.md should mention homebrew install freetype

Changes: https://git.openjdk.java.net/jdk16u/pull/109/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16u&pr=109&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265531
  Stats: 2 lines in 2 files changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk16u/pull/109.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16u pull/109/head:pull/109

PR: https://git.openjdk.java.net/jdk16u/pull/109