Added TERRAFORM_SOURCE_DIR variable to specify terraform code path (#389)

* Added `TERRAFORM_SOURCE_DIR` variable to specify subdir

* Auto Format

* Update README.md

* Auto Format

* Update README.md

Co-authored-by: Andriy Knysh <aknysh@users.noreply.github.com>

* Auto Format

---------

Co-authored-by: cloudpossebot <11232728+cloudpossebot@users.noreply.github.com>
Co-authored-by: Andriy Knysh <aknysh@users.noreply.github.com>

Author: 3 people

README.md

@@ -1,7 +1,7 @@
 
 
 <!-- markdownlint-disable -->
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+<a href="https://cpco.io/homepage"><img src="https://github.com/cloudposse/build-harness/blob/main/.github/banner.png?raw=true" alt="Project Banner"/></a><br/>
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modules/docs/Makefile

@@ -18,7 +18,7 @@ docs/targets.md: docs/deps
 ## Update `docs/terraform.md` from `terraform-docs`
 docs/terraform.md: docs/deps packages/install/terraform-docs
 	@echo "<!-- markdownlint-disable -->" > $@ ; \
-	terraform-docs --lockfile=false md . >> $@ ; \
+	terraform-docs --lockfile=false md .$(TERRAFORM_SOURCE_DIR) >> $@ ; \
 	echo "<!-- markdownlint-restore -->" >> $@
 
 .PHONY : docs/github-action.md