docs: don't use :hg: at the beginning of lines in notes (issue3397)

It seem like docutils 0.8 interpret ':hg:`command`' roles at the beginning of
indented lines in '.. note::' directives as a field that is an invalid argument
to the directive. It fails with 'Error in "note" directive: invalid option
block.' Docutils 0.7 accepted this arguably incorrect markup.

Reflowing the text makes the problem go away. A leading '\ ' could perhaps also
be used to mask the problem.

mercurial/help/patterns.txt

@@ -1,57 +1,57 b''
 Mercurial accepts several notations for identifying one or more files
 at a time.
 
 By default, Mercurial treats filenames as shell-style extended glob
 patterns.
 
 Alternate pattern notations must be specified explicitly.
 
 .. note::
-  Patterns specified in ``.hgignore`` are not rooted. Please see
-  :hg:`help hgignore` for details.
+  Patterns specified in ``.hgignore`` are not rooted. 
+  Please see :hg:`help hgignore` for details.
 
 To use a plain path name without any pattern matching, start it with
 ``path:``. These path names must completely match starting at the
 current repository root.
 
 To use an extended glob, start a name with ``glob:``. Globs are rooted
 at the current directory; a glob such as ``*.c`` will only match files
 in the current directory ending with ``.c``.
 
 The supported glob syntax extensions are ``**`` to match any string
 across path separators and ``{a,b}`` to mean "a or b".
 
 To use a Perl/Python regular expression, start a name with ``re:``.
 Regexp pattern matching is anchored at the root of the repository.
 
 To read name patterns from a file, use ``listfile:`` or ``listfile0:``.
 The latter expects null delimited patterns while the former expects line
 feeds. Each string read from the file is itself treated as a file
 pattern.
 
 Plain examples::
 
   path:foo/bar   a name bar in a directory named foo in the root
                  of the repository
   path:path:name a file or directory named "path:name"
 
 Glob examples::
 
   glob:*.c       any name ending in ".c" in the current directory
   *.c            any name ending in ".c" in the current directory
   **.c           any name ending in ".c" in any subdirectory of the
                  current directory including itself.
   foo/*.c        any name ending in ".c" in the directory foo
   foo/**.c       any name ending in ".c" in any subdirectory of foo
                  including itself.
 
 Regexp examples::
 
   re:.*\.c$      any name ending in ".c", anywhere in the repository
 
 File examples::
 
   listfile:list.txt  read list from list.txt with one file pattern per line
   listfile0:list.txt read list from list.txt with null byte delimiters
 
 See also :hg:`help filesets`.