doc: Coder version range compatibility check

- resolves #114

Author: fioan89

.github/readme/compatibility_check.png

@@ -226,6 +226,16 @@ versions of Gateway we've decided:
   different release channels (ex: `eap` or `beta`), but all of them except the stable channel have to be
   manually configured by users in Gateway - which is super inconvenient.
 
+## Supported Coder versions
+
+`Coder Gateway` includes checks for compatibility with a specified version range. A warning is raised when
+the Coder deployment build version is outside of compatibility range:
+![Compatibility Check with Coder deployment](.github/readme/compatibility_check.png)
+
+The range needs to be manually updated as often as possible. The lowest bound is specified by `minCompatibleCoderVersion`
+property in the [CoderSupportedVersions.properties](src/main/resources/version/CoderSupportedVersions.properties)
+while `maxCompatibleCoderVersion` specifies the upper bound.
+
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