Explain relationship b/w toolchain rule and toolchain_type
Closes
@@ -218,7 +218,11 @@ To define some toolchains for a given toolchain type, we need three things:
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.
+ 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
