Merge branch 'jc/format-patch-rfc-more'

The "--rfc" option of "git format-patch" learned to take an
optional string value to be used in place of "RFC" to tweak the
"[PATCH]" on the subject header.

* jc/format-patch-rfc-more:
  format-patch: "--rfc=-(WIP)" appends to produce [PATCH (WIP)]
  format-patch: allow --rfc to optionally take a value, like --rfc=WIP

Documentation/git-format-patch.txt

@@ -20,7 +20,7 @@ SYNOPSIS
 		   [--in-reply-to=<message-id>] [--suffix=.<sfx>]
 		   [--ignore-if-in-upstream] [--always]
 		   [--cover-from-description=<mode>]
-		   [--rfc] [--subject-prefix=<subject-prefix>]
+		   [--rfc[=<rfc>]] [--subject-prefix=<subject-prefix>]
 		   [(--reroll-count|-v) <n>]
 		   [--to=<email>] [--cc=<email>]
 		   [--[no-]cover-letter] [--quiet]
@@ -238,10 +238,21 @@ the patches (with a value of e.g. "PATCH my-project").
 	value of the `format.filenameMaxLength` configuration
 	variable, or 64 if unconfigured.
 
---rfc::
-	Prepends "RFC" to the subject prefix (producing "RFC PATCH" by
-	default). RFC means "Request For Comments"; use this when sending
-	an experimental patch for discussion rather than application.
+--rfc[=<rfc>]::
+	Prepends the string _<rfc>_ (defaults to "RFC") to
+	the subject prefix.  As the subject prefix defaults to
+	"PATCH", you'll get "RFC PATCH" by default.
++
+RFC means "Request For Comments"; use this when sending
+an experimental patch for discussion rather than application.
+"--rfc=WIP" may also be a useful way to indicate that a patch
+is not complete yet ("WIP" stands for "Work In Progress").
++
+If the convention of the receiving community for a particular extra
+string is to have it _after_ the subject prefix, the string _<rfc>_
+can be prefixed with a dash ("`-`") to signal that the the rest of
+the _<rfc>_ string should be appended to the subject prefix instead,
+e.g., `--rfc='-(WIP)'` results in "PATCH (WIP)".
 
 -v <n>::
 --reroll-count=<n>::