fast-import: Document author/committer/tagger name is optional

The fast-import parser does not validate that the author, committer
or tagger name component contains both a name and an email address.
Therefore the name component has always been optional.  Correct the
documentation to match the implementation.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-fast-import.txt

@@ -311,8 +311,8 @@ change to the project.
 ....
 	'commit' SP <ref> LF
 	mark?
-	('author' SP <name> SP LT <email> GT SP <when> LF)?
-	'committer' SP <name> SP LT <email> GT SP <when> LF
+	('author' (SP <name>)? SP LT <email> GT SP <when> LF)?
+	'committer' (SP <name>)? SP LT <email> GT SP <when> LF
 	data
 	('from' SP <committish> LF)?
 	('merge' SP <committish> LF)?
@@ -657,7 +657,7 @@ lightweight (non-annotated) tags see the `reset` command below.
 ....
 	'tag' SP <name> LF
 	'from' SP <committish> LF
-	'tagger' SP <name> SP LT <email> GT SP <when> LF
+	'tagger' (SP <name>)? SP LT <email> GT SP <when> LF
 	data
 ....
 

fast-import.c

@@ -19,8 +19,8 @@ Format of STDIN stream:
 
   new_commit ::= 'commit' sp ref_str lf
     mark?
-    ('author' sp name sp '<' email '>' sp when lf)?
-    'committer' sp name sp '<' email '>' sp when lf
+    ('author' (sp name)? sp '<' email '>' sp when lf)?
+    'committer' (sp name)? sp '<' email '>' sp when lf
     commit_msg
     ('from' sp committish lf)?
     ('merge' sp committish lf)*
@@ -47,7 +47,7 @@ Format of STDIN stream:
 
   new_tag ::= 'tag' sp tag_str lf
     'from' sp committish lf
-    ('tagger' sp name sp '<' email '>' sp when lf)?
+    ('tagger' (sp name)? sp '<' email '>' sp when lf)?
     tag_msg;
   tag_msg ::= data;