RFR: Added build section [v3]

[Jesper Wilhelmsson]

> Instructions on how to build the JDK.

Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:

  Link to build instructions

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Changes:
  - all: https://git.openjdk.java.net/guide/pull/56/files
  - new: https://git.openjdk.java.net/guide/pull/56/files/3bfcca72..53fe4011

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=guide&pr=56&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=guide&pr=56&range=01-02

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/guide/pull/56.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/56/head:pull/56

PR: https://git.openjdk.java.net/guide/pull/56