Add AGENTS.md file (#20373)

* Add AGENTS.md file

Fixes DOC-14837

See also: https://agents.md

Co-authored-by: Mike Lewis <[email protected]>

Author: rmloveland

src/current/AGENTS.md

@@ -0,0 +1,47 @@
+# AGENTS.md for CockroachDB docs
+
+Hello! We're working together on docs for CockroachDB, a distributed SQL database. The docs are located in Markdown files (with Liquid templates) in various subdirectories of this one.
+
+This file has instructions and general info for working with us on these docs. Please pay close attention to things written here.
+
+Docs for each released version are in subdirectories named for the version, e.g., `v25.4`.
+
+Docs specific to the CockroachDB Cloud product are in `cockroachcloud`.
+
+Docs related to release notes and other release-related matters are in `releases`.
+
+## Style guide
+
+Our style guide lives in `StyleGuide.md` in the root of this repository. Please follow the guidance there carefully when writing docs.
+
+## Include files
+
+To avoid repeating text across different files, we use shared "include files" (or just: "includes") which are referenced using the following syntax.
+
+For includes that apply across versions or products:
+
+```
+{% include common/define-watched-cdc.md %}
+```
+
+For includes that pertain to the CockroachDB Cloud product:
+
+```
+{% include cockroachcloud/metrics-time-interval-selection.md %}
+```
+
+For includes that we can assume only apply to specific versions, though in some cases, their content may be identical across all versions where the file exists:
+
+```
+{% include vXX.Y/misc/cert-auth-using-x509-subject.md %}
+```
+
+Note: The Liquid variable `{{page.version.version}}` resolves to the major version in the path of the page where it is used (e.g. `v25.4`). References to version-specific includes often use this, allowing the same page content that's used across versions to show different versions of an include, based on the current version being rendered. For example, `{% include {{page.version.version}}/misc/cert-auth-using-x509-subject.md %}`.
+  
+The includes are all located in subdirectories of the `_include` directory, i.e.,
+
+- `_include/common` for widely shared things
+- `_include/cockroachcloud` for Cloud
+- `_include/v25.4` for v25.4-specific content
+
+<!-- eof -->