docs: add section about mismatch in TS loading the language service

Adds information about the issue seen in #594 to the README. cc
@ikilinc.

Author: ayazhafiz

README.md

@@ -16,6 +16,19 @@ and external templates including:
 
 Download the extension from [Visual Studio Marketplace](https://marketplace.visualstudio.com/items?itemName=Angular.ng-template).
 
+## Versioning
+
+The langauge service extension uses the `@angular/language-service` package for its backend. This
+package is loaded either from the version bundled with the extension, or from the current workspace
+project the extension is running on. Due to the behavior of TypeScript below version 3.8,
+incompatible versions of the language service may sometimes be loaded. If you are using a version of
+TypeScript below 3.8, we suggest either
+
+- Not installing `@angular/language-service` in your project (recommended; will fallback on the
+    version bundled with the extension)
+- Installing and keeping updates for the latest version of `@angular/language-service`
+
+For further information, please see #594.
 
 ## Installing a particular release build
 
@@ -24,6 +37,7 @@ Download the `.vsix` file for the release that you want to install from the [rel
 *Do not open the .vsix file directly*. Instead, in Visual Studio code, go to the extensions tab. Click on the "..." menu in the upper right corner of the extensions tab, select "Install from vsix..." and then select the .vsix file for the release you just downloaded.
 
 The extension can also be installed with the following command:
+
 ```
 code --install-extension /path/to/ngls.vsix
 ```