[PATCH 3 of 6] help: document about "branches" template keywords

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1538573929 -32400
#      Wed Oct 03 22:38:49 2018 +0900
# Node ID 1d6252375718965479b2602fa7558436a08cbeb1
# Parent  6d44024b584d8e8c35d693eddd87e368aa8ea3dd
help: document about "branches" template keywords

diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1132,6 +1132,18 @@ def branches(ui, repo, active=False, clo
 
     Use the command :hg:`update` to switch to an existing branch.
 
+    .. container:: verbose
+
+      Template:
+
+      The following keywords are supported in addition to the common template
+      keywords and functions such as ``{branch}``. See also
+      :hg:`help templates`.
+
+      :active:  Boolean. True if the branch is active.
+      :closed:  Boolean. True if the branch is closed.
+      :current: Boolean. True if it is the current branch.
+
     Returns 0.
     """