chore: add config / docs for 'pre-commit' support (#103)

Source-Author: Tres Seaver <tseaver@palladion.com>
Source-Date: Tue Dec 1 16:01:20 2020 -0500
Source-Repo: googleapis/synthtool
Source-Sha: 32af6da519a6b042e3da62008e2a75e991efb6b4
Source-Link: https://github.com/googleapis/synthtool/commit/32af6da519a6b042e3da62008e2a75e991efb6b4
diff --git a/synth.metadata b/synth.metadata
index 1d8cb42..e401af9 100644
--- a/synth.metadata
+++ b/synth.metadata
@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-api-core.git",
-        "sha": "fcf261fc3c4c1f28f2fa13d055716cf70d21f6f5"
+        "sha": "93976931f231da6b42304bd117d8481067c55f6a"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "a073c873f3928c561bdf87fdfbf1d081d1998984"
+        "sha": "32af6da519a6b042e3da62008e2a75e991efb6b4"
       }
     }
   ],
@@ -58,6 +58,7 @@
     ".kokoro/test-samples.sh",
     ".kokoro/trampoline.sh",
     ".kokoro/trampoline_v2.sh",
+    ".pre-commit-config.yaml",
     ".trampolinerc",
     "CODE_OF_CONDUCT.md",
     "CONTRIBUTING.rst",