README: add section about making releases

Author: Stephen Gutekanst

README.md

@@ -29,3 +29,11 @@ If you want to develop the CLI, you can install it with `go get`:
 ```
 go get -u github.com/sourcegraph/src-cli/cmd/src
 ```
+
+## Releasing
+
+1. Find the latest version (either via the releases tab on GitHub or via git tags).
+2. `git tag 1.0.0 -a -m 'release v1.0.0'` (replace `1.0.0` with the version you are releasing)
+3. `git push --tags`
+
+Travis will automatically perform the release.