git: openjdk/jdk: 8247591: Document Alpine Linux build steps in OpenJDK build guide

[Alexander Scherbatiy]

Changeset: 508c8a95
Author:    Aleksei Voitylov <avoitylov at openjdk.org>
Committer: Alexander Scherbatiy <alexsch at openjdk.org>
Date:      2020-10-13 09:42:23 +0000
URL:       https://git.openjdk.java.net/jdk/commit/508c8a95

8247591: Document Alpine Linux build steps in OpenJDK build guide

Co-authored-by: Aleksei Voitylov <avoitylov at openjdk.org>
Reviewed-by: erikj

! doc/building.html
! doc/building.md