Add note about supported logstash version to readme

README.md

@@ -8,6 +8,10 @@ The project was created as rewrite of existing awesome application
 which was also written in Go, but it was not maintained for a long time.
 A lot of code was reused from the original project.
 
+**Important:** Because of limited workforces, this project is tested only against a single Logstash version.
+You can check the tested version in [docker-compose.yml](./docker-compose.yml) file.
+Using this exporter with other versions of Logstash may not work properly (although most of the metrics should work).
+
 ## Usage
 
 ### Running the app
@@ -100,7 +104,7 @@ All configuration variables can be checked in the [config directory](./config/).
 #### Available Commands
 
 <!--- GENERATED by ./scripts/add_descriptions_to_readme.sh --->
- 
+
 - `make all`: Builds binary executables for all OS (Win, Darwin, Linux).
 - `make run`: Runs the Go Exporter application.
 - `make build-linux`: Builds a binary executable for Linux.
@@ -121,7 +125,7 @@ All configuration variables can be checked in the [config directory](./config/).
 - `make install-helm-readme`: Installs readme-generator-for-helm tool.
 - `make helm-readme`: Generates Helm chart README.md file.
 - `make help`: Shows info about available commands.
- 
+
 <!--- **************************************************** --->
 
 #### File Structure
@@ -132,87 +136,87 @@ The binary executables are saved in the out directory.
 #### Example Usage
 
 <!--- GENERATED by ./scripts/add_descriptions_to_readme.sh --->
- 
+
 Builds binary executables for all OS (Win, Darwin, Linux):
- 
+
     make all
- 
+
 Runs the Go Exporter application:
- 
+
     make run
- 
+
 Builds a binary executable for Linux:
- 
+
     make build-linux
- 
+
 Builds a binary executable for Darwin:
- 
+
     make build-darwin
- 
+
 Builds a binary executable for Windows:
- 
+
     make build-windows
- 
+
 Builds a Docker image for the Go Exporter application:
- 
+
     make build-docker
- 
+
 Builds a multi-arch Docker image (`amd64` and `arm64`):
- 
+
     make build-docker-multi
- 
+
 Deletes all binary executables in the out directory:
- 
+
     make clean
- 
+
 Runs all tests:
- 
+
     make test
- 
+
 Displays test coverage report:
- 
+
     make test-coverage
- 
+
 Starts a Docker-compose configuration:
- 
+
     make compose
- 
+
 Starts a Docker-compose configuration until it's ready:
- 
+
     make wait-for-compose
- 
+
 Stops a Docker-compose configuration:
- 
+
     make compose-down
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+
 Verifies the metrics from the Go Exporter application:
- 
+
     make verify-metrics
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+
 Pulls the Docker image from the registry:
- 
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     make pull
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+
 Shows logs from the Docker-compose configuration:
- 
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     make logs
- 
+
 Minifies the binary executables:
- 
+
     make minify
- 
+
 Installs readme-generator-for-helm tool:
- 
+
     make install-helm-readme
- 
+
 Generates Helm chart README.md file:
- 
+
     make helm-readme
- 
+
 Shows info about available commands:
- 
+
     make help
- 
+
 <!--- **************************************************** --->
 
 ## Helper Scripts