Add purpose to README

README.md

@@ -1,5 +1,20 @@
-# nested_maps
-A small Terraform module to build a nested map for for_each resource declarations
+# terraform-nested-maps
+
+A small Terraform module to build a nested map to use with`for_each` resource declarations.
+
+I wanted to condence 100+ lines of remote data sources to pull in resources, and I wanted to utilize the new `for_each` feature.
+
+This could easily go in one file and not be a module, but this allows me to use the same method for things like `vpc_peering_connections`.
+
+I wanted to use this module method because it now gives me really neat names like `aws_security_group.this['cms-dev']`. This makes it pretty easy to move and refactor these as they still have the same name:
+
+```bash
+tf plan > plan.tfplan
+cat plan.tfplan | grep "destroyed" # creates output like `data.aws_security_group.cms-dev`
+cat plan.tfplan | grep "created" # creates output like `data.aws_security_group.this["cms-dev"]`
+```
+
+You can then take the above `grep'd` output and paste it into a Text Editor and match up the names for easy state move commands.
 
 <!-- BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
 ## Requirements