[doc] Update lint documentation

Signed-off-by: Michael Schaffner <msf@opentitan.org>
diff --git a/tool_requirements.py b/tool_requirements.py
index 7777c6e..4a1a0f2 100644
--- a/tool_requirements.py
+++ b/tool_requirements.py
@@ -6,4 +6,5 @@
 # and inserted into the documentation.
 __TOOL_REQUIREMENTS__ = {
     'verilator': '4.028',
+    'verible': '0.0-375-g7d55b5b',
 }