content: update about and future pages to talk about source track (#1254

)

a quick cleanup pass to reflect the new source track in the drafts folder.

docs/spec/draft/about.md

@@ -1,6 +1,6 @@
 ---
 title: About SLSA
-description: With supply chain attacks on the rise, a shared vocabulary and universal framework is needed to provide incremental guidance to harden supply chains for more secure software production. This page introduces the main concepts behind SLSA and explains how it can help anyone involved in producing, consuming, or providing infrastructure for software. 
+description: With supply chain attacks on the rise, a shared vocabulary and universal framework is needed to provide incremental guidance to harden supply chains for more secure software production. This page introduces the main concepts behind SLSA and explains how it can help anyone involved in producing, consuming, or providing infrastructure for software.
 ---
 
 This page is an introduction to SLSA and its concepts. If you're new
@@ -102,9 +102,7 @@ chain between them.
 
 We talk about SLSA in terms of [tracks and levels](levels.md).
 A SLSA track focuses on a particular aspect of a supply chain, such as the Build
-Track. SLSA v1.0 consists of only a single track ([Build](levels.md#build-track)), but future versions of
-SLSA will add tracks that cover other parts of the software supply chain, such
-as how source code is managed.
+Track.
 
 Within each track, ascending levels indicate increasingly hardened security
 practices. Higher levels provide better guarantees against supply chain threats,
@@ -130,9 +128,7 @@ important to consider together with SLSA such as:
     source code followed secure coding practices.
 -   Producer trust: SLSA does not address organizations that intentionally
     produce malicious software, but it can reduce insider risks within an
-    organization you trust. SLSA's Build Track protects against tampering during
-    or after the build, and [future SLSA tracks](future-directions.md) intend to
-    protect against unauthorized modifications of source code and dependencies.
+    organization you trust.
 -   Transitive trust for dependencies: the SLSA level of an artifact is
     independent of the level of its dependencies. You can use SLSA recursively to
     also judge an artifact's dependencies on their own, but there is

docs/spec/draft/future-directions.md

@@ -36,20 +36,12 @@ following requirements, which **may or may not** be part of a future Build L4:
 
 ## Source track
 
-A Source track could provide protection against tampering of the source code
+A Source track will provide protection against tampering of the source code
 prior to the build.
 
-The initial [draft version (v0.1)](../v0.1/requirements.md#source-requirements)
-of SLSA included the following source requirements, which **may or may not**
-form the basis for a future Source track:
-
--   Strong authentication of author and reviewer identities, such as 2-factor
-    authentication using a hardware security key, to resist account and
-    credential compromise.
--   Retention of the source code to allow for after-the-fact inspection and
-    future rebuilds.
--   Mandatory two-person review of all changes to the source to prevent a single
-    compromised actor or account from introducing malicious changes.
+The current [draft version (v1.1)](source-requirements.md) describes levels
+of increasing tamper resistance and ways consumers might verify properties
+of source revisions using SLSA source provenance attestations.
 
 </section>