git-add --interactive: add documentation

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-add.txt

@@ -7,7 +7,7 @@ git-add - Add file contents to the changeset to be committed next
 
 SYNOPSIS
 --------
-'git-add' [-n] [-v] [--] <file>...
+'git-add' [-n] [-v] [--interactive] [--] <file>...
 
 DESCRIPTION
 -----------
@@ -43,6 +43,10 @@ OPTIONS
 -v::
         Be verbose.
 
+\--interactive::
+	Add modified contents in the working tree interactively to
+	the index.
+
 \--::
 	This option can be used to separate command-line options from
 	the list of files, (useful when filenames might be mistaken
@@ -67,6 +71,119 @@ git-add git-*.sh::
 	(i.e. you are listing the files explicitly), it does not
 	consider `subdir/git-foo.sh`.
 
+Interactive mode
+----------------
+When the command enters the interactive mode, it shows the
+output of the 'status' subcommand, and then goes into ints
+interactive command loop.
+
+The command loop shows the list of subcommands available, and
+gives a prompt "What now> ".  In general, when the prompt ends
+with a single '>', you can pick only one of the choices given
+and type return, like this:
+
+------------
+    *** Commands ***
+      1: status       2: update       3: revert       4: add untracked
+      5: patch        6: diff         7: quit         8: help
+    What now> 1
+------------
+
+You also could say "s" or "sta" or "status" above as long as the
+choice is unique.
+
+The main command loop has 6 subcommands (plus help and quit).
+
+status::
+
+   This shows the change between HEAD and index (i.e. what will be
+   committed if you say "git commit"), and between index and
+   working tree files (i.e. what you could stage further before
+   "git commit" using "git-add") for each path.  A sample output
+   looks like this:
++
+------------
+              staged     unstaged path
+     1:       binary      nothing foo.png
+     2:     +403/-35        +1/-1 git-add--interactive.perl
+------------
++
+It shows that foo.png has differences from HEAD (but that is
+binary so line count cannot be shown) and there is no
+difference between indexed copy and the working tree
+version (if the working tree version were also different,
+'binary' would have been shown in place of 'nothing').  The
+other file, git-add--interactive.perl, has 403 lines added
+and 35 lines deleted if you commit what is in the index, but
+working tree file has further modifications (one addition and
+one deletion).
+
+update::
+
+   This shows the status information and gives prompt
+   "Update>>".  When the prompt ends with double '>>', you can
+   make more than one selection, concatenated with whitespace or
+   comma.  Also you can say ranges.  E.g. "2-5 7,9" to choose
+   2,3,4,5,7,9 from the list.  You can say '*' to choose
+   everything.
++
+What you chose are then highlighted with '*',
+like this:
++
+------------
+           staged     unstaged path
+  1:       binary      nothing foo.png
+* 2:     +403/-35        +1/-1 git-add--interactive.perl
+------------
++
+To remove selection, prefix the input with `-`
+like this:
++
+------------
+Update>> -2
+------------
++
+After making the selection, answer with an empty line to stage the
+contents of working tree files for selected paths in the index.
+
+revert::
+
+  This has a very similar UI to 'update', and the staged
+  information for selected paths are reverted to that of the
+  HEAD version.  Reverting new paths makes them untracked.
+
+add untracked::
+
+  This has a very similar UI to 'update' and
+  'revert', and lets you add untracked paths to the index.
+
+patch::
+
+  This lets you choose one path out of 'status' like selection.
+  After choosing the path, it presents diff between the index
+  and the working tree file and asks you if you want to stage
+  the change of each hunk.  You can say:
+
+       y - add the change from that hunk to index
+       n - do not add the change from that hunk to index
+       a - add the change from that hunk and all the rest to index
+       d - do not the change from that hunk nor any of the rest to index
+       j - do not decide on this hunk now, and view the next
+           undecided hunk
+       J - do not decide on this hunk now, and view the next hunk
+       k - do not decide on this hunk now, and view the previous
+           undecided hunk
+       K - do not decide on this hunk now, and view the previous hunk
++
+After deciding the fate for all hunks, if there is any hunk
+that was chosen, the index is updated with the selected hunks.
+
+diff::
+
+  This lets you review what will be committed (i.e. between
+  HEAD and index).
+
+
 See Also
 --------
 gitlink:git-status[1]

builtin-add.c

@@ -12,7 +12,7 @@
 #include "cache-tree.h"
 
 static const char builtin_add_usage[] =
-"git-add [-n] [-v] <filepattern>...";
+"git-add [-n] [-v] [--interactive] [--] <filepattern>...";
 
 static void prune_directory(struct dir_struct *dir, const char **pathspec, int prefix)
 {