docs: SECURITY.md says how to report a vulnerability (#65)

SECURITY.md asks for vulnerabilities to be reported privately, through GitHub's private vulnerability reporting or by email to karl-einarb@outlook.com.

docs/development.md: the "Pull requests" heading is now "How changes land". The section covers squash merges, PR titles and branch protection, not how to send one.

Reviewed-on: #65
Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

README.md

@@ -92,7 +92,7 @@ use most:
   secret
 - [Config](docs/config.md): every option, themes, layered configs, the
   state file
-- [Development](docs/development.md): building, tests, pull requests and
+- [Development](docs/development.md): building, tests, how changes land and
   releasing
 
 ## Privacy

SECURITY.md

@@ -0,0 +1,11 @@
+# Security
+
+Please report a vulnerability privately, not in a public issue:
+
+- on GitHub, with **Report a vulnerability** under the
+  [Security tab](https://github.com/karleinarb/lazysecrets/security), or
+- by email to karl-einarb@outlook.com.
+
+Say what's affected, how to reproduce it and the version
+(`lazysecrets --version`). Fixes go into the next release, and only the
+latest release gets them.

docs/development.md

@@ -22,7 +22,7 @@ Development builds show `dev-<commit>` as their version (`-dirty` with
 uncommitted changes); `go install …@v0.2.0` shows the tag, releases the
 version they were built for.
 
-## Pull requests
+## How changes land
 
 Pull requests into `main` are squash-merged, so each is one commit titled
 like the PR. The title is a [conventional commit](https://www.conventionalcommits.org)