Added a description of how to back port changes to old versions

process/how_to_backport_changes.md

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+### The process of back port changes to old release branches is as follows:
+
+In order to back port changes to the old release branches you need to create your own branch,
+push your changes to this branch, create a pull request with your changes and, when it will be approved,
+merge your changes into the oldest release branch which you want to change.
+
+Then you should create a branch that merges the previous release branch into the next release branch,
+create a pull request and approve it. And do the same for each branch till the `main` branch.
+
+For example let's say we need to back port changes to project `leap` which has two release branches `release/3.1`, 
+`release/3.2` and a `main` branch. Here is what we should do:
+
+- Create a branch with the changes
+
+- Create a PR into `release/3.1` from that branch
+
+  - Once approved, merge into `release/3.1`
+
+- Create a branch that merges `release/3.1` into `release/3.2`
+
+- Create a PR into `release/3.2` from that branch
+
+  - Once approved, merge into `release/3.2`
+
+- Create a branch that merges `release/3.2` into main
+
+- Create a PR into `main` from that branch
+
+  - Once approved, merge into `main`
+
+