Finished lesson on the options argument.

lessons/options-argument/lesson.md

@@ -1,20 +1,32 @@
 # Options argument
 
 There is another attribute that is automatically provided by the  module system, `options`.
-Options 
+`options` provides information about all of the option declarations in the module.
+It has much more information than `config` which only gives you the final value.
+It can tell you what the type is, what the default value is, whether or not it is defined, and many more things.
 
 !!! note
     This is the `options` function argument attribute which is not to be confused by the `options` attribute where we declare options.
 
+Let us take a look at using the information provided by `options` to create conditional logic.
+In our `options.nix` file, we have the same option declarations that we have seen in previous lessons.
+However, we have change how `greeting` is defined.
+Now the definition is conditionally generated depending on which options we define.
+If we set a value for `name`, then we will get an additional line in our output.
+If we do not, then that line is completely omitted.
+
 [//]: # (./options.nix)
 
+In our `config.nix`, we define values for `name` and `origin`, but not `title`.
+This is fine because use of the title definition is contingent on whether or not it is defined—remember nix is *lazy*!
+
 [//]: # (./config.nix)
 
 Setup an `eval.nix` to evaluate our modules and return the `config.greeting` attribute.
 
 [//]: # (./eval.nix)
 
-Create a `run.sh` run script to evalute the `eval.nix` file.
+Create a `run.sh` run script to evaluate the `eval.nix` file.
 
 [//]: # (./run.sh)