Added metadata for appendixes

Signed-off-by: Serhii Horodilov <sgorodil@gmail.com>

Author: shorodilov

src/appx/blog.txt

@@ -1 +1,6 @@
+.. meta::
+    :description: Specification for Django blog training project
+    :author: Serhii Horodilov
+    :keywords: python, django, blog, project, training
+
 .. include:: /../blog/docs/spec.rst

src/appx/code_edit.txt

@@ -1,4 +1,7 @@
-.. appendix
+.. meta::
+    :description: Code editors and IDEs for Python
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: python, editor, ide
 
 ############
 Code Editors

src/appx/conv_store.txt

@@ -1 +1,6 @@
+.. meta::
+    :description: Convenience store challenge
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: python, basics, oop, object-oriented programming
+
 .. include:: /../problem-sets/src/conv_store/challenge.rst

src/appx/env_path.txt

@@ -1,4 +1,7 @@
-.. appendix
+.. meta::
+    :description: Setting up environment variables
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: settings, environment, variables
 
 ###############################
 Issue - System Environment PATH

src/appx/precedence.txt

@@ -1,7 +1,7 @@
-.. appendix
-
-.. todo:
-    https://docs.python.org/3/reference/expressions.html#operator-precedence
+.. meta::
+    :description: Operator precedence in Python
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: python, basics, operator, precedence
 
 ###################
 Operator Precedence

src/appx/printf.txt

@@ -1,4 +1,7 @@
-.. appendix
+.. meta::
+    :description: Formatted strings usage in Python
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: python, string, formatting
 
 .. todo: add code examples
 

src/appx/wtk.txt

@@ -1 +1,6 @@
+.. meta::
+    :description: Knights, thieves and wizards game project
+    :author: Serhii Horodilov sgorodil@gmail.com
+    :keywords: python, game, oop, object-oriented programming
+
 .. include:: /../problem-sets/src/wtk/challenge.rst