[v3] Update Markdown files to latest spec (#33)

All Markdown files should, from this point on, start with a level one heading.
See https://github.com/exercism/configlet/issues/150 for the rationale behind these changes.

The full specification can be found [here](https://github.com/exercism/docs/blob/main/contributing/standards/markdown.md).

config/exercise-readme-insert.md

@@ -0,0 +1,2 @@
+# exercise readme insert
+

docs/ABOUT.md

@@ -0,0 +1,2 @@
+# About
+

docs/INSTALLATION.md

@@ -0,0 +1,2 @@
+# Installation
+

docs/LEARNING.md

@@ -0,0 +1,2 @@
+# Learning
+

docs/RESOURCES.md

@@ -0,0 +1,2 @@
+# Resources
+

docs/TESTS.md

@@ -0,0 +1,2 @@
+# Tests
+