readme: move section about testing to contributing guide

There is a guide made by Github with recommendations how to make project
healthy for contributors [1]. One of them is a contributing guide with
steps for new contributors. Knowledge about running tests in a project
is not needed to all people who will read our README, so I moved this
section to contributing guide.

Part of #123

1. https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions

Author: ligurio

CONTRIBUTING.md

@@ -0,0 +1,29 @@
+# Contribution Guide
+
+## Running tests
+
+You need to [install Tarantool](https://tarantool.io/en/download/) to run tests.
+See the Installation section in the README for requirements.
+
+To install test dependencies (such as the
+[tarantool/queue](https://github.com/tarantool/queue) module), run:
+```bash
+make deps
+```
+
+To run tests for the main package and each subpackage:
+```bash
+make test
+```
+
+The tests set up all required `tarantool` processes before run and clean up
+afterwards.
+
+If you want to run the tests for a specific package:
+```bash
+make test-<SUBDIR>
+```
+For example, for running tests in `multi`, `uuid` and `main` packages, call
+```bash
+make test-multi test-uuid test-main
+```

README.md

@@ -26,7 +26,7 @@ faster than other packages according to public benchmarks.
 * [API reference](#api-reference)
 * [Walking\-through example in Go](#walking-through-example-in-go)
 * [Help](#help)
-* [Tests](#tests)
+* [Contributing](#contributing)
 * [Alternative connectors](#alternative-connectors)
 
 ## Installation
@@ -164,30 +164,10 @@ To contact `go-tarantool` developers on any problems, create an issue at
 The developers of the [Tarantool server](http://github.com/tarantool/tarantool)
 will also be happy to provide advice or receive feedback.
 
-## Tests
+## Contributing
 
-You need to [install Tarantool](https://www.tarantool.io/en/download/) to run tests.
-See [Installation](#installation) section for requirements.
-
-To install test dependencies (like [tarantool/queue](https://github.com/tarantool/queue) module), run
-```bash
-make deps
-```
-
-To run tests for the main package and each subpackage, call
-```bash
-make test
-```
-Tests set up all required `tarantool` processes before run and clean up after.
-
-If you want to run a specific package tests, call
-```bash
-make test-<SUBDIR>
-```
-For example, for running tests in `multi`, `uuid` and `main` packages, call
-```bash
-make test-multi test-uuid test-main
-```
+See [the contributing guide](CONTRIBUTING.md) for detailed instructions on how
+to get started with our project.
 
 ## Alternative connectors