docs: create README files for directories

Signed-off-by: André Jaenisch <andre.jaenisch@posteo.de>

adrs/README.md

@@ -0,0 +1,9 @@
+# Architectural Decision Records
+
+During development, many decisions are to be made.
+Since it is one aim of js13kgames to learn more things, I want to write down
+what my thoughts were when choosing certain tooling and what else could have
+been an option.
+
+I tend to look at these more from an engineering perspective than a Game Dev
+one.

gdd/README.md

@@ -0,0 +1,6 @@
+# Game Design Document
+
+A game design document is normally kept in professional setups.
+However, I've heard of it so often and found a book describing it in more
+detail, that I want to try it out. Perhaps it helps me make it under the top
+100?!

journal/README.md

@@ -0,0 +1,8 @@
+# Journal
+
+I tend to put too much into my Postmortem, so this year, I try to keep a
+journal and update it daily as I go along.
+
+## Entries
+
+- [13th August 2021](./2021-08-13.md)