Added some terraform questions and answers

README.md

@@ -2359,6 +2359,12 @@ The benefits of Terraform over the other tools:
 
 <details>
 <summary>Explain what is "Terraform configuration"</summary><br><b>
+A configuration is a root module along with a tree of child modules that are called as dependencies from the root module.
+</b></details>
+
+<details>
+<summary>What is HCL?</summary><br><b>
+HCL stands for Hashicorp Conviguration Language. It is the language Hashicorp made to use as the configuration language for a number of its tools, including terraform.
 </b></details>
 
 <details>
@@ -2390,6 +2396,7 @@ It keeps track of the IDs of created resources so that Terraform knows what it i
 
 <code>terraform init</code> scans your code to figure which providers are you using and download them.
 <code>terraform plan</code> will let you see what terraform is about to do before actually doing it.
+<code>terraform validate</code> checks if configuration is syntactically valid and internally consistent within a directory.
 <code>terraform apply</code> will provision the resources specified in the .tf files.
 </b></details>
 
@@ -2424,18 +2431,29 @@ It's a resource which was successfully created but failed during provisioning. T
 <details>
 <summary>What types of variables are supported in Terraform?</summary><br><b>
 
-String
-Integer
-Map
-List
+string
+number
+bool
+list(<TYPE>)
+set(<TYPE>)
+map(<TYPE>)
+object({<ATTR_NAME> = <TYPE>, ... })
+tuple([<TYPE>, ...])
 </b></details>
 
 <details>
 <summary>What is a data source? In what scenarios for example would need to use it?</summary><br><b>
+Data sources lookup or compute values that can be used elsewhere in terraform configuration.
+
+There are quite a few cases you might need to use them:
+* you want to reference resources not managed through terraform
+* you want to reference resources managed by a different terraform module
+* you want to cleanly compute a value with typechecking, such as with <code>aws_iam_policy_document</code>
 </b></details>
 
 <details>
 <summary>What are output variables and what <code>terraform output</code> does?</summary><br><b>
+Output variables are named values that are sourced from the attributes of a module. They are stored in terraform state, and can be used by other modules through <code>remote_state</code>
 </b></details>
 
 <details>
@@ -2472,6 +2490,17 @@ List
  The random provider aids in generating numeric or alphabetic characters to use as a prefix or suffix for a desired named identifier.
 </b></details>
 
+<details>
+<summary>How do you test a terraform module?</summary><br><b>
+  Many examples are acceptable, but the most common answer would likely to be using the tool <code>terratest</code>, and to test that a module can be initialized, can create resources, and can destroy those resources cleanly.
+</b></details>
+
+<details>
+<summary>Aside from <code>.tfvars</code> files or CLI arguments, how can you inject dependencies from other modules?</summary><br><b>
+  The built-in terraform way would be to use <code>remote-state</code> to lookup the outputs from other modules.
+  It is also common in the community to use a tool called <code>terragrunt</code> to explicitly inject variables between modules.
+</b></details>
+
 ## Docker
 
 <a name="docker-beginner"></a>