added readme

README.md

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+# fcmp - compare file identity
+
+A shell utils that compares files for identity with `mmap()` and `memcmp()`.
+
+# Usage
+`fcmp` produces no output, but success is indicated by its return code.
+
+```shell
+$ fcmp file1 file2 && echo "Equal!"
+```
+
+| Code | Meaning                                                      |
+|------|--------------------------------------------------------------|
+| 0    | The files are equal                                          |
+| 1    | The files are unequal                                        |
+| 2    | The files have unequal lengths, and therefor must be unequal |
+| -1   | There was an error                                           |
+
+Therefor you can use this in shell scripts easily:
+
+``` shell
+# Example
+
+if fcmp "$1" "$2"; then
+    echo "Files are equal!"
+else
+    echo "Files are not equal!"
+fi
+```
+
+# License
+GPL'd with <3