Rewrite documentation

[conorsch]

With the addition of several Ansible roles for managing the build and install process for the grsecurity-patched kernel, we need to update the documentation to explain how the roles should be used. In particular, the grsecurity_patch_type and grsecurity_build_strategy vars should be explained in detail.

The step-by-step build docs currently in build.md can be folded into the docs to explain how to approach the grsecurity_build_strategy=manual use case, which is currently the default behavior of the build role.

• [x] required vars (e.g. grsecurity_install_deb_package)
• [x] default vars
• [x] example playbooks
• [x] further reading resources
  • [x] linux kernel compilation
  • [x] grsecurity/pax
• [x] rename repo grsec -> ansible-role-grsecurity
• [x] declare master the main branch (actually necessary due to confusion in #35 and #46)
• [x] break up docs:
  • [x] securedrop-specific docs into separate document
  • [x] manual build steps in separate document

[conorsch]

The new docs should include a brief explanation about the non-standard bundled nature of this role. We'll defer discussion of separating the build and install roles into distinct repositories for now. Docs checklist: [moved to OP so github displays a progress bar on the issues page]

[conorsch]

Working on this now.