Added README

Fortune for sink's current commit: Future curse − 末凶

README.md

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+# `sink` - sinks all input into `/dev/null`
+
+Re-routes `stdin`, `stdout` (and optionally, `stderr`) to `/dev/null`.
+
+## Building
+
+Run `make && sudo make install` to build with full optimisations and install `sink` to `/usr/local/bin/sink`. (run `sudo make uninstall` to remove.)
+
+To build for debugging, run `make debug`. 
+
+### Compiler flags
+`-DREPLACE_STDERR` - Add to `CFLAGS` when building a target to re-route the program's `stderr` stream to the sink as well. By default, it is closed after the other streams have been successfully rewritten.
+
+### Installation
+The program must have been built before installation, and installation and uninstallation must be done as root.
+By default, `make install` will install `sink` to `$(DESTDIR)$(PREFIX)/bin`. You can override this by setting `PREFIX=/path/to/usr make install`
+
+To install a different target, for example, `debug`, run `make debug && sudo make install OUTPUT=sink-debug` (`OUTPUT` is the binary name.)
+*NOTE*: You must specify the same `OUTPUT` value for `make uninstall` if done this way.
+
+### Target CPU
+If building on a VPS, you may want to run `TARGET_ARCH= make` instead of `make`, to build for generic CPU instead of the default native target for optimised (`release`) builds.
+
+### Static linkage
+By default, the program is entirely statically linked. To override this, run `SHARED=yes make`, for any building target.
+
+### Stripping
+To build optimised without stripping the symbol table, run `make release` or `make STRIP=:`.
+For installing *without* stripping the symbol table, run `sudo make install STRIP=true`; the effect is the same as `STRIP=:` which does not work for the `install` target.
+
+### Other targets
+`sink` (**default**): stripped `release` target. output: `sink`
+`release`: optimised build. output: `sink-release`
+`debug`: unoptimised build with debuginfo. output: `sink-debug`
+`clean`: remove all previous object and binary output files
+
+### Environment variables
+* `PREFIX` - The installation path prefix. Defaults to `/usr/local` if not set.
+* `SHARED` - set to "yes" to prevent passing `--static` to cc
+* `TARGET_ARCH` - target arch (`-march=`), or set `TARGET_ARCH=` to force set to generic target. (default [release only]: `native`)
+* `CFLAGS`, `COMMON_FLAGS` - passthrough to cc
+* `LDFLAGS` - passthrough to ld
+* `DEBUG_CFLAGS`, `DEBUG_LDFLAGS` - passthrough to cc / ld on target `debug`
+* `RELEASE_CFLAGS`, `RELEASE_LDFLAGS` - passthrough to cc / ld on target `release`
+
+#### Make overridable only
+* `STRIP` - Strip command for default output (stripped release) target (`make sink`). set `make STRIP=:` to prevent stripping entirely. (NOTE: When using `make install`, `STRIP=:` will not work, instead, paradoxically, set `STRIP=true`, they have the same effect for all targets)
+* `OUTPUT` - The name of the output binary from the default target, and the binary that `install`/`uninstall` targets look for.