Make markdownlint happy about README.md

```
README.md:1 MD041/first-line-heading/first-line-h1 First line in file should be a top level heading [Context: "![Run all tests](https://githu..."]
README.md:2 MD022/blanks-around-headings/blanks-around-headers Headings should be surrounded by blank lines [Expected: 1; Actual: 0; Above] [Context: "# getssl"]
```

README.md

@@ -1,6 +1,7 @@
-![Run all tests](https://github.com/srvrco/getssl/workflows/Run%20all%20tests/badge.svg) ![shellcheck](https://github.com/srvrco/getssl/workflows/shellcheck/badge.svg)
 # getssl
 
+![Run all tests](https://github.com/srvrco/getssl/workflows/Run%20all%20tests/badge.svg) ![shellcheck](https://github.com/srvrco/getssl/workflows/shellcheck/badge.svg)
+
 Obtain SSL certificates from the letsencrypt.org ACME server. Suitable
 for automating the process on remote servers.