Documentation: generate manual pages for core ssh commands

Extend the documentation tool chain to produce manual pages for
core ssh commands.

To generate manual pages:
cd <gerrit>/Documentation/man
make

Test it locally with: man -l gerrit-review
or deploy it system wide:
Copy *.1 to /usr/local/share/man/man1 and test it with
man gerrit-review

Change-Id: I2f2801e55e8a626f60df2abe985f2e4da88b30a7

ReleaseNotes/ReleaseNotes-2.6.txt

diff --git a/ReleaseNotes/ReleaseNotes-2.6.txt b/ReleaseNotes/ReleaseNotes-2.6.txt
index 64b25df..e2c9c45 100644
--- a/ReleaseNotes/ReleaseNotes-2.6.txt
+++ b/ReleaseNotes/ReleaseNotes-2.6.txt
@@ -150,6 +150,7 @@
 Corrected references to `refs/changes` in the access control documentation.
 
 * Various minor grammatical and formatting corrections.
+* Manual pages can be optionally created/installed for core gerrit ssh commands.
 
 Developer And Maintainer Documentation
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~