Merge branch 'jn/ignore-doc' into maint

* jn/ignore-doc:
  Documentation: point to related commands from gitignore
  Documentation: split gitignore page into sections

Author: gitster

Documentation/gitignore.txt

@@ -14,11 +14,8 @@ DESCRIPTION
 
 A `gitignore` file specifies intentionally untracked files that
 git should ignore.
-Note that all the `gitignore` files really concern only files
-that are not already tracked by git;
-in order to ignore uncommitted changes in already tracked files,
-please refer to the 'git update-index --assume-unchanged'
-documentation.
+Files already tracked by git are not affected; see the NOTES
+below for details.
 
 Each line in a `gitignore` file specifies a pattern.
 When deciding whether to ignore a path, git normally checks
@@ -62,7 +59,8 @@ files specified by command-line options.  Higher-level git
 tools, such as 'git status' and 'git add',
 use patterns from the sources specified above.
 
-Patterns have the following format:
+PATTERN FORMAT
+--------------
 
  - A blank line matches no files, so it can serve as a separator
    for readability.
@@ -98,7 +96,20 @@ Patterns have the following format:
    For example, "/{asterisk}.c" matches "cat-file.c" but not
    "mozilla-sha1/sha1.c".
 
-An example:
+NOTES
+-----
+
+The purpose of gitignore files is to ensure that certain files
+not tracked by git remain untracked.
+
+To ignore uncommitted changes in a file that is already tracked,
+use 'git update-index {litdd}assume-unchanged'.
+
+To stop tracking a file that is currently tracked, use
+'git rm --cached'.
+
+EXAMPLES
+--------
 
 --------------------------------------------------------------
     $ git status
@@ -140,6 +151,11 @@ Another example:
 The second .gitignore prevents git from ignoring
 `arch/foo/kernel/vmlinux.lds.S`.
 
+SEE ALSO
+--------
+linkgit:git-rm[1], linkgit:git-update-index[1],
+linkgit:gitrepository-layout[5]
+
 Documentation
 -------------
 Documentation by David Greaves, Junio C Hamano, Josh Triplett,