added README

README.md

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+# Compile-time `memfrob()`
+
+glibc has a function in `string.h` called `memfrob()` which applies ROT13 to an arbitrary byte buffer.
+This small C++20 header allows you to do this at compile time to trivially obscure string literals without the literal itself appearing in the binary anywhere at all.
+
+# Usage
+The literals can be created and stored as a sized `char` array, or as a C string pointer.
+
+``` c++
+#include "cfrob.hpp"
+
+const auto easter_egg = "Something cool"_frob;
+const char* c_like_easter_egg = "Something cool"_frob;
+```
+
+To reverse just apply ROT13 on to the string again.
+
+``` c++
+auto string2 = strdup(easter_egg);
+memfrob(string2, strlen(easter_egg));
+// `string2` now contains the string "Something cool"
+free(string2);
+```
+
+## Test
+Run `make test` to build and run the test that ensures the original string literal does not appear anywhere in the outputted binary. 
+
+# License
+Public domain.