docs(readme): add initial with build instructions (#15)

Author: mcomella

README.md

@@ -0,0 +1,20 @@
+# zealdocs.github.io
+https://zealdocs.org/: web documentation for [Zeal, an offline documentation browser][zeal].
+
+## Development
+To build this static site, you need the following dependencies:
+- `jekyll` (`v3.1.6` from Ubuntu 18.04 works correctly)
+
+To perform a one-off build, run:
+```sh
+jekyll build
+```
+
+To build any time a source code file changes and locally host the results at `http://127.0.0.1:4000/`, run:
+```sh
+jekyll serve
+```
+
+For more information on jekyll usage, see [the official jekyll documentation](https://jekyllrb.com/docs/usage/).
+
+[zeal]: https://github.com/zealdocs/zeal