doc: update the readme.

Author: iocanel

README.md

@@ -1 +1,22 @@
-# cli
+# cli 
+
+A simple shell library with cli utilities.
+
+## hasflag
+ Checks if a flag is present in the arguments. Returns 'true' if its present, or nothing otherwise.
+ 
+Example:
+    
+    hasflag --help $*
+    
+## readopt
+Read the value of an option. It returns the next argument following the option.
+
+Example:
+    
+    readopt --log-level $*
+
+## or
+Returns the first argument if not empty, the second otherwise.
+
+    value=$(or $candidate "default value")