RFR: Add info about MANPATH to README.

[Magnus Ihse Bursie]

Add info about MANPATH to README.

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Commit messages:
 - Add info about MANPATH to README.

Changes: https://git.openjdk.java.net/skara/pull/680/files
 Webrev: https://webrevs.openjdk.java.net/skara/680/webrev.00
  Stats: 9 lines in 1 file changed: 9 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/680.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/680/head:pull/680

PR: https://git.openjdk.java.net/skara/pull/680