Adds a readme.md

Author: joeljuca

readme.md

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+# numeric-only
+
+Bash utility function that strips non-numeric characters from its arguments.
+
+## Usage
+
+```sh
+numeric-only "123.456.789"  # => 123456789
+numeric-only 123 456 789    # => 123456789
+numeric-only 12. 34 5.6 .78 # => 12345678
+```
+
+## License
+
+[ISC](license)