README.md: Add example

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 centaur
 =======
 
-centaur is an ELF executable editing toolkit.
+centaur is an ELF executable editing toolkit, focusing on code
+injection and function detouring.
 
 
-Features
---------
+Example
+-------
 
-At the moment, centaur provides:
-  - Code injection from object files into executables
-  - Function detouring in executables
+Injecting an object file into a program and detouring a function
+could hardly be simpler:
+
+    elfucli --input program \
+            --reladd objfile.o \
+            --detour oldfunc,newfunc \
+            --output program_modified
+
+elfucli parses the command line parameters one by one like a script.
+
+In this example, it:
+
+  1. Loads the executable `program` containing the function `oldfunc`.
+  2. Injects an object file containing the function `newfunc`.
+  3. Overwrites the beginning of `oldfunc` with a jump to `newfunc`.
+  4. Writes the modified program to `program_modified`.
+
+This functionality is exposed by the underlying `libelfu` via a C API,
+at the same high level. `elfucli` serves as an example application for
+it and doubles as a handy scalpel for ELF files.
+
+More examples can be found in the testsuite.
 
 
 Build instructions, Credits, License, ...
 -----------------------------------------
 
-See the docs/ directory for more documentation.
+See the docs/ directory for all other documentation.