Added a README file.

README.md

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+# Cleanup utility
+
+The utility will keep up to **N** (defaults to 5) of the latest subdirectories and removes all the others.
+
+Modification time will be used when determining the sort order of subdirectories.
+
+## Usage examples
+
+* `cleanup <PATH-TO-DIRECTORY> -l 5` keeps up to 5 latest subdirectories of the path provided
+* `cleanup <PATH-TO-DIRECTORY>` keeps up to 5 (default value) subdirectories of the path provided
+* `cleanup -v` displays the version information of the utility script
+* `cleanup` - displays help text of the utility script
+
+## Building
+
+Build the binaries by running `./go-executable-build.bash` and check the **data** directory for resulting binaries. You
+may change the defined platform as needed.
+
+Default platforms are `linux/386`, `linux/amd64` and `darwin/amd64`.