docs: add style guide to `run_tests`

Signed-off-by: Mitchell Buckley <mitchell.alan.buckley@gmail.com>

ROOTS

@@ -10,3 +10,4 @@ lib
 lib/Word_Lib
 lib/sep_algebra
 lib/EVTutorial
+docs

docs/Makefile

@@ -0,0 +1,14 @@
+#
+# Copyright 2021, Data61, CSIRO (ABN 41 687 119 230)
+#
+# SPDX-License-Identifier: GPL-2.0-only
+#
+
+default: heaps
+all: heaps
+
+heaps: Docs
+
+HEAPS += Docs
+
+include ../misc/isa-common.mk

docs/ROOT

@@ -0,0 +1,16 @@
+(*
+ * Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
+ *
+ * SPDX-License-Identifier: GPL-2.0-only
+ *)
+
+(*
+ * Miscellaneous text documentation files which can also be
+ * checked as Isabelle/HOL theories.
+ *)
+
+chapter Docs
+
+session Docs = HOL +
+  theories
+    "Style"

docs/tests.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0"?>
+<!--
+     Copyright 2020, Data61, CSIRO (ABN 41 687 119 230)
+
+     SPDX-License-Identifier: GPL-2.0-only
+-->
+
+<!--
+
+     Regression Specification File
+
+     See "misc/regression/tests.xml" for a description of the file
+     format.
+
+-->
+<testsuite depends="isabelle" cpu-timeout="600">
+    <test name="Docs">make Docs</test>
+</testsuite>