[v3] Update Markdown files to latest spec (#92)

* [v3] Add level one headings to Markdown files.

All Markdown files should, from this point on, start with a level one heading.
See exercism/configlet#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).

* [v3] Markdown sub-headings must be parent level incremented by one.

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

docs/ABOUT.md

@@ -1,3 +1,5 @@
+# About
+
 [Pony](http://www.ponylang.org) is an object-oriented, actor-model, capabilities-secure programming language focused on geting stuff done.
 
 It's object-oriented because it has classes and objects, like Python, Java, C++, and many other languages. It's actor-model because it has actors (similar to Erlang or Akka). These behave like objects, but they can also execute code asynchronously. Actors make Pony awesome.

docs/INSTALLATION.md

@@ -1,12 +1,12 @@
-## Installing the Pony Compiler
+# Installing the Pony Compiler
 
-### Homebrew on Mac OS X
+## Homebrew on Mac OS X
 
 ```bash
 brew update
 brew install ponyc
 ```
 
-### Other Platforms
+## Other Platforms
 
 Instructions for installing Pony can be found in the [ponyc installation](https://github.com/ponylang/ponyc/blob/master/README.md#installation)

docs/LEARNING.md

@@ -1,4 +1,4 @@
-## Resources for Learning Pony:
+# Resources for Learning Pony:
 
 - [The Pony Tutorial](https://tutorial.ponylang.org/)
 - [Pony Patterns](https://patterns.ponylang.org/)

docs/RESOURCES.md

@@ -1,4 +1,4 @@
-## Resources for Learning Pony
+# Resources for Learning Pony
 
 - [The Pony Tutorial](https://tutorial.ponylang.org/)
 - [Pony Patterns](https://patterns.ponylang.org/)

docs/TESTS.md

@@ -1,4 +1,4 @@
-## Running tests
+# Running tests
 
 To compile and run the tests, just run the following in your exercise directory:
 ```bash