Update env table with project-id (#634)

updates env table to include project id. on hold for tfc merge

Author: drewmullen

content/terraform-docs-common/docs/cloud-docs/run/run-environment.mdx

@@ -124,6 +124,7 @@ HCP Terraform automatically injects the following environment variables for each
 | `TFC_CONFIGURATION_VERSION_GIT_COMMIT_SHA` | The full commit hash of the commit that the associated Terraform configuration version was ingressed from.                           | `abcd1234...`                   |
 | `TFC_CONFIGURATION_VERSION_GIT_TAG`        | The name of the tag that the associated Terraform configuration version was ingressed from.                                          | `v0.1.0`                        |
 | `TFC_PROJECT_NAME`                         | The name of the project used in this run.                                                                                            | `proj-name`                     |
+| `TFC_PROJECT_ID`.                          | The id of the project used in this run.                                                                                              | `proj-91XJpbLvbdohC6RD`         |
 
 They are also available as Terraform input variables by defining a variable with the same name. For example: