Convert RELEASING to Markdown and add instruction for GitHub release

Author: jhasse

RELEASING renamed to RELEASING.md

@@ -1,33 +1,41 @@
 Notes to myself on all the steps to make for a Ninja release.
 
-Push new release branch:
+### Push new release branch:
 1. Run afl-fuzz for a day or so and run ninja_test
 2. Consider sending a heads-up to the ninja-build mailing list first
 3. Make sure branches 'master' and 'release' are synced up locally
 4. Update src/version.cc with new version (with ".git"), then
-       git commit -am 'mark this 1.5.0.git'
+   ```
+   git commit -am 'mark this 1.5.0.git'
+   ```
 5. git checkout release; git merge master
 6. Fix version number in src/version.cc (it will likely conflict in the above)
 7. Fix version in doc/manual.asciidoc (exists only on release branch)
 8. commit, tag, push (don't forget to push --tags)
-       git commit -am v1.5.0; git push origin release
-       git tag v1.5.0; git push --tags
-       # Push the 1.5.0.git change on master too:
-       git checkout master; git push origin master
+   ```
+   git commit -am v1.5.0; git push origin release
+   git tag v1.5.0; git push --tags
+   # Push the 1.5.0.git change on master too:
+   git checkout master; git push origin master
+   ```
 9. Construct release notes from prior notes
-   credits: git shortlog -s --no-merges REV..
 
-Release on github:
-1. https://github.com/blog/1547-release-your-software
-   Add binaries to https://github.com/ninja-build/ninja/releases
+   credits: `git shortlog -s --no-merges REV..`
 
-Make announcement on mailing list:
+
+### Release on GitHub:
+1. Go to [Tags](https://github.com/ninja-build/ninja/tags)
+2. Open the newly created tag and select "Create release from tag"
+3. Create the release which will trigger a build which automatically attaches
+   the binaries
+
+### Make announcement on mailing list:
 1. copy old mail
 
-Update website:
+### Update website:
 1. Make sure your ninja checkout is on the v1.5.0 tag
 2. Clone https://github.com/ninja-build/ninja-build.github.io
 3. In that repo, `./update-docs.sh`
 4. Update index.html with newest version and link to release notes
-5. git commit -m 'run update-docs.sh, 1.5.0 release'
-6. git push origin master
+5. `git commit -m 'run update-docs.sh, 1.5.0 release'`
+6. `git push origin master`