[patch] README: Fix a typo

[kaneko y]

I found a typo.

commit 995a1b7453725e65b3e26d49773f6ebfa286e5a8 (origin/fix_README,
fix_README)
Author: Yuichiro Kaneko <address@hidden>
Date:   Wed Oct 23 09:21:52 2019 +0900

    README: Fix a typo

    * README: Fix a typo. Git command name is submodule.

diff --git a/README b/README
index 0d4c257d..e5a19d8d 100644
--- a/README
+++ b/README
@@ -4,7 +4,7 @@ This package contains the GNU Bison parser generator.
 ## Build from git
 Here are basic installation instructions for a repository checkout:

-    $ git submodules update --init
+    $ git submodule update --init
     $ ./bootstrap

 then proceed with the usual 'configure && make' steps.