Merge pull request #10421 from tamsky/patch-1

Explain list-type variables, and their use

website/source/intro/getting-started/variables.html.md

@@ -56,7 +56,8 @@ the AWS provider with the given variables.
 ## Assigning Variables
 
 There are multiple ways to assign variables. Below is also the order
-in which variable values are chosen. The following is the descending order of precedence in which variables are considered.
+in which variable values are chosen. The following is the descending order
+of precedence in which variables are considered.
 
 #### Command-line flags
 
@@ -109,6 +110,8 @@ $ terraform plan \
   -var-file="secret.tfvars" \
   -var-file="production.tfvars"
 ```
+-> **Note**: Environment variables can only populate string-type variables. 
+List and map type variables must be populated via one of the other mechanisms.
 
 #### UI Input
 
@@ -126,6 +129,23 @@ If no value is assigned to a variable via any of these methods and the
 variable has a `default` key in its declaration, that value will be used
 for the variable.
 
+<a id="lists"></a>
+## Lists
+
+Lists are defined either explicitly or implicity
+```
+# implicitly by using brackets [...]
+variable "cidrs" { default = [] }
+
+# explicitly
+variable "cidrs" { type = "list" }
+```
+
+You can specify lists in a `terraform.tfvars` file:
+```
+cidrs = [ "10.0.0.0/16", "10.1.0.0/16" ]
+```
+
 <a id="mappings"></a>
 <a id="maps"></a>
 ## Maps