Update README

README.md

+PostSRSd
+========
+
 About
-=====
+-----
+
 PostSRSd provides the Sender Rewriting Scheme (SRS) via TCP-based 
 lookup tables for Postfix. SRS is needed if your mail server acts
 as forwarder. 
 
+
+Sender Rewriting Scheme Crash Course
+------------------------------------
 Imagine your server receives a mail from alice@example.com
 that is to be forwarded. If example.com uses the Sender Policy Framework 
 to indicate that all legit mails originate from their server, your 
 your own domain, e.g. 
 SRS0+xxxx=yy=example.com=alice@yourdomain.org (forward SRS). If the
 mail is bounced later and a notification arrives, you can extract the
-original address from the rewritten one (revere SRS) and return the
+original address from the rewritten one (reverse SRS) and return the
 notification to the sender. You might notice that the reverse SRS can
 be abused to turn your server into an open relay. For this reason, xxxx
 and yy are a cryptographic signature and a time stamp. If the signature
 does not match, the address is forged and the mail can be discarded.
 
 Building
-========
+--------
+
 PostSRSd requires a POSIX compatible system and CMake to build. 
 Optionally, help2man is used to create a manual page.
 
 For convenience, a Makefile fragment is provided which calls CMake with
 the recommended command line options. Just run `make`.
 
+Alternatively, you can control many aspects of the build manually:
+
+    mkdir build
+    cd build
+    cmake .. <options>
+    make
+    make install
+
+The CMake script defines a number of options in addition to the
+standard CMake flags. Use `-D<option>=<value>` to override the defaults.
+
+*   `GENERATE_SRS_SECRET` (default: `ON`). Generate a random secret on install.
+*   `USE_APPARMOR` (default: `OFF`): Install an AppArmor profile for the daemon.
+*   `INIT_FLAVOR` (default: auto-detect). Select the appriopriate startup 
+    script type. Must be one of (`upstart`,`sysv-lsb`,`sysv-redhat`) or `none`.
+*   `CHROOT_DIR` (default: `${CMAKE_INSTALL_PREFIX}/lib/postsrsd`). Chroot jail
+    for the daemon.
+*   `SYSCONF_DIR` (default: `/etc`). Location of system configuration files.
+*   `CONFIG_DIR` (default: `${SYSCONF_DIR}/default`). Install destination for
+    the postsrsd settings.
+*   `DOC_DIR` (default: `${CMAKE_INSTALL_PREFIX}/share/doc/postsrsd`). Install
+    destination for documentation files.
+
 Installing
-==========
+----------
+
 Run `make install` as root to install the daemon and the configuration
 files.
 
 Configuration
-=============
-The configuration is located in `/etc/default/postsrsd`. You must store
+-------------
+
+The configuration is located in `/etc/default/postsrsd` by default. You must store
 at least one secret key in `/etc/postsrsd.secret`. The installer tries to generate
 one from `/dev/urandom`. Be careful that no one can guess your secret,
 because anyone who knows it can use your mail server as open relay!