Readme: Add terraform-lsp section

Author: radeksimko

README.md

@@ -45,3 +45,24 @@ Please follow the [relevant guide for your IDE](./docs/USAGE.md).
 - [Zhe Cheng](https://github.com/njuCZ) - research, design, prototyping assistance
 - [Julio Sueiras](https://github.com/juliosueiras) - particularly his [language server implementation](https://github.com/juliosueiras/terraform-lsp)
 
+
+## `terraform-ls` VS `terraform-lsp`
+
+Both HashiCorp and [the maintainer](https://github.com/juliosueiras) of [`terraform-lsp`](https://github.com/juliosueiras/terraform-lsp)
+expressed interest in collaborating on a language server and are working
+towards a _long-term_ goal of a single stable and feature-complete implementation.
+
+For the time being both projects continue to exist, giving users the choice:
+
+- `terraform-ls` providing
+  - overall stability (by relying only on public APIs)
+  - compatibility with any provider and any Terraform `>=0.12.0`
+  - currently less features
+    - due to project being younger and relying on public APIs which may not
+      offer the same functionality yet
+
+- `terraform-lsp` providing
+  - currently more features
+  - compatibility with a single particular Terraform (`0.12.20` at time of writing)
+    - configs designed for other `0.12` versions may work, but interpretation may be inaccurate
+  - less stability (due to reliance on Terraform's own internal packages)