help: add sections for revsets

mercurial/help/revsets.txt

@@ -12,11 +12,17 Special characters can be used in quoted
 e.g., ``\n`` is interpreted as a newline. To prevent them from being
 interpreted, strings can be prefixed with ``r``, e.g. ``r'...'``.
 
+Prefix
+======
+
 There is a single prefix operator:
 
 ``not x``
   Changesets not in x. Short form is ``! x``.
 
+Infix
+=====
+
 These are the supported infix operators:
 
 ``x::y``
@@ -71,16 +77,24 These are the supported infix operators:
     in this case. This matches against all of "issue 1234", "issue:1234",
     "issue1234" and "bug(1234)".
 
+Postfix
+=======
+
 There is a single postfix operator:
 
 ``x^``
   Equivalent to ``x^1``, the first parent of each changeset in x.
 
+Predicates
+==========
 
 The following predicates are supported:
 
 .. predicatesmarker
 
+Aliases
+=======
+
 New predicates (known as "aliases") can be defined, using any combination of
 existing predicates or other aliases. An alias definition looks like::
 
@@ -102,6 +116,8 For example,
 defines three aliases, ``h``, ``d``, and ``rs``. ``rs(0:tip, author)`` is
 exactly equivalent to ``reverse(sort(0:tip, author))``.
 
+Equivalents
+===========
 
 Command line equivalents for :hg:`log`::
 
@@ -114,6 +130,9 Command line equivalents for :hg:`log`::
   -P x  ->  !::x
   -l x  ->  limit(expr, x)
 
+Examples
+========
+
 Some sample queries:
 
 - Changesets on the default branch::