fix(README.md): add missing step

The `watchman` project requires `automake`.
feat(basics.org): Add new tutorial basics.
fix(basics): update example

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(org-batch): hack for invoking Lean web interface
feat(juicy-ace-editor): make editor read-only by default
feat(org-batch): add support for marking the "main" part of an example
using '-- BEGIN' and '-- END'
feat(basics): update tutorial with '--BEGIN'/'--END' delimiters
feat(tutorial.css): nicer button
feat(tutorial.css): change color scheme to match subatomic mode
feat(test.sh): add test script for tutorials
feat(basics): add Boolean section
fix(basics): remove redundant exercise numbers
fix(code.css): hide ACE editor cursor
feat(basics): add documentation for functions and natural numbers