docs: fix typo in readme (#761)

* docs: fix typo in readme

Signed-off-by: Daniel Perez Alvarez <danielpza@protonmail.com>

* Update README.md

Co-authored-by: Frazer Smith <frazer.dev@icloud.com>
Signed-off-by: Daniel Perez Alvarez <danielpza@protonmail.com>

---------

Signed-off-by: Daniel Perez Alvarez <danielpza@protonmail.com>
Co-authored-by: Frazer Smith <frazer.dev@icloud.com>

Author: danielpza

README.md

@@ -21,7 +21,7 @@ project:
 $ fastify
 ```
 
-Will print an help:
+Which will print a help message:
 
 ```
 Fastify command line interface, available commands are: