Add RELEASING.md with necessary instructions

RELEASING.md

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+# Releasing new version
+
+## Step-by-step
+
+In order to release a new version, there are several steps that must happen:
+
+ 0. make sure all issues (in GitHub and in JIRA) targeted to the version are resolved
+ 1. create a pull request in which you change the [version string](https://github.com/modcluster/mod_proxy_cluster/blob/main/native/include/mod_proxy_cluster.h#L21) according to the format described in [another section](#version-naming-conventions)
+ 2. get review and merge the pull request
+ 3. release the version through GH release functionality with the tag corresponding to version from the pull request
+ 4. mark the corresponding version released in [JIRA](https://issues.redhat.com/projects/MODCLUSTER?release-page) as well
+
+
+## Version naming conventions
+
+Version string must have the following format:
+
+* `major.minor.micro.Alpha<number>`
+* `major.minor.micro.Beta<number>`
+* `major.minor.micro.CR<number>`
+* `major.minor.micro.Final`
+
+where `<number>` is a mandatory numerical value starting from `1`. Any version marked `Final` must not have a number. If there
+is any issue with such a version, just increase a micro version and go through the process again.