hello: add page (#4586)

pages/linux/hello.md

@@ -0,0 +1,16 @@
+# hello
+
+> Print "Hello, world!", "hello, world" or a customizable text.
+> More information: <https://www.gnu.org/software/hello/>.
+
+- Print "Hello, world!":
+
+`hello`
+
+- Print "hello, world", the traditional type:
+
+`hello --traditional`
+
+- Print a text message:
+
+`hello --greeting="{{greeting_text}}"`