Add documentation for rpm packaging (#278)

packaging/rpm/README.md

@@ -0,0 +1,40 @@
+# Building RPMs
+
+The `Makefile` contains steps that will build RPMs using the locally-configured `rpmbuild` environment.
+
+However, a better approach is to use [mock](https://github.com/rpm-software-management/mock/wiki) which ensures all packages are built in a standard, reproducible environment, and also allows building for targets other than that of the local machine.
+
+The steps to build RPMs with mock are:
+
+* Create tarball + generate spec file from template
+
+    ```bash
+    cd packaging/rpm
+    make clean && make buildtargz
+    ```
+
+* Create SRPM from tarball and spec file
+
+    ```bash
+    mock -r epel-7-x86_64 --buildsrpm --spec qpsmtpd.spec --sources build
+    mv /var/lib/mock/epel-7-x86_64/result/*.src.rpm build
+    ```
+
+3. Build RPMs from SRPM
+
+    ```bash
+    mock -r epel-7-x86_64 build/*.src.rpm
+    mv /var/lib/mock/epel-7-x86_64/result/*.rpm build
+    ```
+
+This builds packages named using the content of the `PACKAGE`, `VERSION`, and `RELEASE` files in the `packaging/rpm` directory.
+
+These can be overridden on the command-line when building the tarball.
+
+For example, to append the local git commit hash to the `RELEASE`:
+
+```bash
+make clean && make buildtargz RELEASE="$(<"RELEASE").$(git rev-parse --short HEAD)"
+```
+
+This will produce a tarball named something like `qpsmtpd-0.96-1.83b6aaf.tar.gz`