Doc: add more detail for git-format-patch

In git-format-patch.txt, we were missing some key user information.
First of all, document the special value of `--base=auto`.

Next, while we're at it, surround option arguments with <> and change
existing names such as "Message-Id" to "message id", which conforms with
how existing documentation is written.

Finally, document the `format.outputDirectory` config and change
`format.coverletter` to use camel case.

Signed-off-by: Denton Liu <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Denton-L

Documentation/git-format-patch.txt

@@ -17,9 +17,9 @@ SYNOPSIS
 		   [--signature-file=<file>]
 		   [-n | --numbered | -N | --no-numbered]
 		   [--start-number <n>] [--numbered-files]
-		   [--in-reply-to=Message-Id] [--suffix=.<sfx>]
+		   [--in-reply-to=<message id>] [--suffix=.<sfx>]
 		   [--ignore-if-in-upstream]
-		   [--rfc] [--subject-prefix=Subject-Prefix]
+		   [--rfc] [--subject-prefix=<subject prefix>]
 		   [(--reroll-count|-v) <n>]
 		   [--to=<email>] [--cc=<email>]
 		   [--[no-]cover-letter] [--quiet]
@@ -159,9 +159,9 @@ Beware that the default for 'git send-email' is to thread emails
 itself.  If you want `git format-patch` to take care of threading, you
 will want to ensure that threading is disabled for `git send-email`.
 
---in-reply-to=Message-Id::
+--in-reply-to=<message id>::
 	Make the first mail (or all the mails with `--no-thread`) appear as a
-	reply to the given Message-Id, which avoids breaking threads to
+	reply to the given <message id>, which avoids breaking threads to
 	provide a new patch series.
 
 --ignore-if-in-upstream::
@@ -171,9 +171,9 @@ will want to ensure that threading is disabled for `git send-email`.
 	patches being generated, and any patch that matches is
 	ignored.
 
---subject-prefix=<Subject-Prefix>::
+--subject-prefix=<subject prefix>::
 	Instead of the standard '[PATCH]' prefix in the subject
-	line, instead use '[<Subject-Prefix>]'. This
+	line, instead use '[<subject prefix>]'. This
 	allows for useful naming of a patch series, and can be
 	combined with the `--numbered` option.
 
@@ -314,7 +314,8 @@ you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.
 --base=<commit>::
 	Record the base tree information to identify the state the
 	patch series applies to.  See the BASE TREE INFORMATION section
-	below for details.
+	below for details. If <commit> is "auto", a base commit is
+	automatically chosen.
 
 --root::
 	Treat the revision argument as a <revision range>, even if it
@@ -330,8 +331,9 @@ CONFIGURATION
 -------------
 You can specify extra mail header lines to be added to each message,
 defaults for the subject prefix and file suffix, number patches when
-outputting more than one patch, add "To" or "Cc:" headers, configure
-attachments, and sign off patches with configuration variables.
+outputting more than one patch, add "To:" or "Cc:" headers, configure
+attachments, change the patch output directory, and sign off patches
+with configuration variables.
 
 ------------
 [format]
@@ -343,7 +345,8 @@ attachments, and sign off patches with configuration variables.
 	cc = <email>
 	attach [ = mime-boundary-string ]
 	signOff = true
-	coverletter = auto
+	outputDirectory = <directory>
+	coverLetter = auto
 ------------