[PATCH] docs/devel/writing-qmp-commands.txt: Fix docs

[Zihao Chang]

Fix the example of add qmp hello-world example.
Without ":", make will report error:
../qapi/misc.json:573:2: line should end with ':'

Signed-off-by: Zihao Chang <changzihao1@huawei.com>
---
 docs/devel/writing-qmp-commands.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/devel/writing-qmp-commands.txt 
b/docs/devel/writing-qmp-commands.txt
index 46a6c48683..28984686c9 100644
--- a/docs/devel/writing-qmp-commands.txt
+++ b/docs/devel/writing-qmp-commands.txt
@@ -243,7 +243,7 @@ There are many examples of such documentation in the schema 
file already, but
 here goes "hello-world"'s new entry for qapi/misc.json:
 
 ##
-# @hello-world
+# @hello-world:
 #
 # Print a client provided string to the standard output stream.
 #
-- 
2.23.0