Echo available options for help

[D-K-E]

I know the interface and the overall structure of the program is not complicated, however it would be really beneficial if lit.sh shows available options and some information about how to use them, when it is called without arguments something like:

$ ./lit.sh
--------------------------------------------------------------------------------
| lit.sh: a simple preprocessor for literate programming
| Example:  
| ./lit.sh dev/myfile.cpp.md -o src/
|
| List of Available options
| -H                     shows this screen
| -o --output            specifies the output directory
| ...
|
| For bugs and suggestions: github.com/vijithassar/lit
|  ...
-------------------------------------------------------------------------------