_content/doc/install: document minimum bootstrap versions

Fixes golang/go#65654
Updates golang/go#54265
Updates golang/go#44505

Change-Id: Ia1c9b50a2f66b67db43e8dcd21b1002b66cf30fa
Reviewed-on: https://go-review.googlesource.com/c/website/+/562619
Auto-Submit: Robert Findley <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

_content/doc/install/source.html

@@ -129,6 +129,19 @@ <h2 id="go14">Install Go compiler binaries for bootstrap</h2>
 root of a Go installation to use to build the new Go toolchain;
 <code>$GOROOT_BOOTSTRAP/bin/go</code> should be the go command to use.</p>
 
+<p>
+The minimum version of Go required depends on the target version of Go:
+</p>
+
+<ul>
+<li> Go &lt;= 1.4: a C toolchain.
+<li> 1.5 &lt;= Go &lt;= 1.19: a Go 1.4 compiler.
+<li> 1.20 &lt;= Go &lt;= 1.21: a Go 1.17 compiler.
+<li> 1.22 &lt;= Go &lt;= 1.23: a Go 1.20 compiler.
+<li> Going forward, Go version 1.N will require a Go 1.M compiler, 
+where M is N-2 rounded down to an even number. Example: Go 1.24 and 1.25 require Go 1.22.
+</ul>
+
 <p>
 There are four possible ways to obtain a bootstrap toolchain:
 </p>
@@ -149,7 +162,7 @@ <h3 id="bootstrapFromBinaryRelease">Bootstrap toolchain from binary release</h3>
 <p>
 To use a binary release as a bootstrap toolchain, see
 <a href="/dl/">the downloads page</a> or use any other
-packaged Go distribution.
+packaged Go distribution meeting the minimum version requirements.
 </p>
 
 <h3 id="bootstrapFromCrosscompiledSource">Bootstrap toolchain from cross-compiled source</h3>