Update common Prometheus files

Signed-off-by: prombot <prometheus-team@googlegroups.com>

.github/workflows/golangci-lint.yml

@@ -0,0 +1,29 @@
+name: golangci-lint
+on:
+  push:
+    paths:
+      - "go.sum"
+      - "go.mod"
+      - "**.go"
+      - "scripts/errcheck_excludes.txt"
+      - ".github/workflows/golangci-lint.yml"
+  pull_request:
+    paths:
+      - "go.sum"
+      - "go.mod"
+      - "**.go"
+      - "scripts/errcheck_excludes.txt"
+      - ".github/workflows/golangci-lint.yml"
+
+jobs:
+  golangci:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Lint
+        uses: golangci/golangci-lint-action@v2
+        with:
+          version: v1.42.0

CODE_OF_CONDUCT.md

@@ -0,0 +1,3 @@
+## Prometheus Community Code of Conduct
+
+Prometheus follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).

SECURITY.md

@@ -0,0 +1,6 @@
+# Reporting a security issue
+
+The Prometheus security policy, including how to report vulnerabilities, can be
+found here:
+
+https://prometheus.io/docs/operating/security/