Add instructions for building and running host tools.

This change adds a new section "Building and Running the Tools" to the
disassembly guide, explaining how to build `oatdump` and `dex2oat` from
the Android tree and how to run them from the output directory.

The examples are updated to use the full path to the binaries.

Subsequent sections are renumbered accordingly.

Flag: EXEMPT DOCS_ONLY
Change-Id: I4c8c0508f5e62650a226ca085683f00ca5c1ac11