Add document for 'false' value for CLI flag

Boolean flags can only take arguments via '--flag=[true|false]' or for
short names (if available) '-f=[true|false]'. You cannot use
'--flag [true|false]' nor can you use the shorthand '-f [true|false]'.

Signed-off-by: Khosrow Moossavi <khos2ow@gmail.com>

docs/user-guide/how-to.md

@@ -8,6 +8,16 @@ weight: 140
 toc: true
 ---
 
+## CLI Flag 'false' value
+
+Boolean flags can only take arguments via `--flag=[true|false]` or for short names
+(if available) `-f=[true|false]`. You cannot use `--flag [true|false]` nor can you
+use the shorthand `-f [true|false]` as it will result in the following error:
+
+```text
+Error: accepts 1 arg(s), received 2
+```
+
 ## Visibility of Sections
 
 Output generated by `terraform-docs` consists of different [sections] which are