chore(publish): add publish instructions to publish.sh

publish.sh

@@ -1 +1,10 @@
-npm run build_npm && npm publish dist
+# To publish angularfire2 to npm, run the following steps
+# Edit the version in package.json
+# Run npm changelog to generate the new changelog (and check the changelog)
+# git commit the changelog and package.json changes
+# git tag <new version>
+# git push <new version> && git push <current branch>
+# Log in to npm: npm login
+# Run this script: ./publish.sh
+
+npm run build_npm && npm publish dist