docs(readme): describe Unix shell framework and tested platforms

Author: rdavid

AGENTS.md

@@ -1,8 +1,10 @@
 # Guidelines
 
-`shellbase` is a POSIX-oriented shell framework (`lib/base.sh`) that scripts
-source for logging, validation, signal handling, garbage collection, and
-concurrent-instance support.
+`shellbase` is a Unix shell framework (`lib/base.sh`) for logging, validation,
+signal handling, garbage collection, and concurrent instances.
+It follows POSIX, the Portable Operating System Interface, and runs on any
+Unix-like system.
+Sourcing it gives a script a set of global variables and functions.
 Read the shared rules at
 https://raw.githubusercontent.com/rdavid/prompt/master/README.txt
 before starting any task, unless they are already loaded.
@@ -27,8 +29,8 @@ This project uses `redo` (or `goredo`) as the primary task runner.
 
 - `redo all`: run the default build target.
 - `redo lint`: run `actionlint`, `agent-rules-lint`, `checkmake`, `conform`,
-  `dash`, `hadolint`, `mksh`, `reuse`, `shellcheck`, `shfmt`, `typos`, `vale`,
-  `yamllint`, and `zizmor`.
+  `dash`, `gitleaks`, `hadolint`, `mksh`, `reuse`, `shellcheck`, `shfmt`,
+  `typos`, `vale`, `yamllint`, and `zizmor`.
 - `redo test`: execute unit tests against the shells installed locally.
 - `redo test-container`: run the test suite inside the supported container
   images.

README.adoc

@@ -90,14 +90,17 @@ endif::[]
 
 == About
 
-`shellbase` is a POSIX shell framework for logging, validation, signal
+`shellbase` is a Unix shell framework for logging, validation, signal
 handling, garbage collection, and concurrent instances.
-It runs on any Unix-like system.
+It follows POSIX, the Portable Operating System Interface, and runs on any
+Unix-like system.
+Continuous integration tests it on FreeBSD, macOS, and Linux distributions
+such as Alpine, Arch Linux, Debian, Fedora, and Red Hat UBI.
 ifndef::pages-build[]
 The framework also has a {url-pages}[website].
 endif::[]
 
-`shellbase` defines global variables and functions.
+Sourcing `shellbase` gives a script a set of global variables and functions.
 Clients may call any function without the `base_` prefix.
 The public functions are, in alphabetical order:
 {url-base}#L71[`aud_only`],