RFR: Added build section [v2]

[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:

  Fixed review comments

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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/ce51dd33..3bfcca72

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=guide&pr=56&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=guide&pr=56&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 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