Explain relationship b/w toolchain rule and toolchain_type
Closes #12854.
PiperOrigin-RevId: 352865787
diff --git a/site/docs/toolchains.md b/site/docs/toolchains.md
index 70ec79d..efe8233 100644
--- a/site/docs/toolchains.md
+++ b/site/docs/toolchains.md
@@ -217,8 +217,12 @@
suite for different platforms.
3. For each such target, an associated target of the generic
-[`toolchain`](be/platform.html#toolchain)
-rule, to provide metadata used by the toolchain framework.
+ [`toolchain`](be/platform.html#toolchain)
+ rule, to provide metadata used by the toolchain framework. This `toolchain`
+ target also refers to the `toolchain_type` associated with this toolchain.
+ This means that a given `\_toolchain` rule could be associated with any
+ `toolchain_type`, and that only in a `toolchain` instance that uses
+ this `\_toolchain` rule that the rule is associated with a `toolchain_type`.
For our running example, here's a definition for a `bar_toolchain` rule. Our
example has only a compiler, but other tools such as a linker could also be
