Added instructions for the alias command

Created the alias.md file, containing some examples of the use of
aliases. Hope you like.

common/alias.md

@@ -0,0 +1,26 @@
+# alias
+
+> Creates an alias for a word when used 
+> as the first word of a command
+
+- creating a generic alias
+
+`alias {{word}}="{{command}}"`
+
+- remove an aliased command
+
+`unalias {{word}}`
+
+- full list of aliased words
+
+`alias -p`
+
+> Some usefull alias commands
+
+- turning rm an interative command
+
+`alias {{rm}}="{{rm -i}}"`
+
+- overriding la as ls -a
+
+`alias {{la}}="{{ls -a}}"`