update man page

Author: miku

README.md

@@ -139,6 +139,7 @@ It's in [AUR](https://aur.archlinux.org/packages/zek-bin/), too.
 ```shell
 $ zek -h
 Usage of zek:
+  -B    use a fixed banner string (e.g. for CI)
   -C    emit less compact struct
   -F    skip formatting
   -P string

docs/zek.md

@@ -33,6 +33,9 @@ at https://www.onlinetool.io/xmltogo/.
 
 # OPTIONS
 
+-B
+:  Use a fixed banner string (e.g. for CI).
+
 -C
 :  Emit less compact representation. This mimicks the former default setting.