Merge pull request #78 from aegershman/patch-1

Add clarification to pre param

README.md

@@ -217,6 +217,8 @@ be one of:
   type, (e.g. `alpha` vs. `beta`), the type is switched and the prerelease
   version is reset to `1`. If the version is *not* already a pre-release, then
   `pre` is added, starting at `1`.
+
+  The value of `pre` can be anything you like; the value will be `pre`-pended (_hah_) to a numeric value. For example, `pre: build` will result in a semver of `x.y.z-build.<number>`, `pre: alpha` becomes `x.y.z-alpha.<number>`, and `pre: my-preferred-naming-convention` becomes `x.y.z-my-preferred-naming-convention.<number>`
 
 ### Running the tests