Update README

README.md

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 # grex
-A command-line tool for generating regular expressions that match user-provided input strings
+
+*grex* is a small command-line utility that is meant to simplify the often complicated and tedious task of creating regular expressions. It does so by automatically generating regular expressions from user-provided input strings that match the generated expression.
+
+In its very early stage, this tool is a Rust port of [*regexgen*](https://github.com/devongovett/regexgen) which has been implemented in JavaScript and runs in a Node.js environment. The plan is, however, to add much more functionality to *grex* than *regexgen* provides. The development of the latter was ceased more than two years ago. Compared to *regexgen*, *grex* is currently lacking support for character classes. This feature will be added in the next version.
+
+## Features
+- literals
+- detection of common prefixes and suffixes
+- alternation using `|` operator
+- repetition using `?` quantifier
+- concatenation of all of the former
+
+## How to use
+```
+$ grex -h
+grex 0.1.0
+Peter M. Stahl <pemistahl@gmail.com>
+grex generates regular expressions that match user-provided input strings.
+
+USAGE:
+    grex <input>...
+
+FLAGS:
+    -h, --help       Prints help information
+    -V, --version    Prints version information
+
+ARGS:
+    <input>... 
+``` 
+### Some examples
+```
+$ grex abc def
+abc|def
+
+$ grex a ab abc
+a(bc?)?
+
+$ grex thankful thoughtful
+th(ought|ank)ful
+
+$ grex 2.0-3.5 2.5-6.0
+2\.(0\-3\.5|5\-6\.0)
+```