fix: redo descriptions and add tags

Signed-off-by: Matej Focko <mfocko@redhat.com>

ib002/02-algorithms-correctness/postcondition-ambiguity.md

@@ -1,8 +1,12 @@
 ---
 title: Vague postconditions and proving correctness of algorithms
 description: |
-  Practical example that shows how precise postconditions can help with both
-  debugging and testing of the code.
+  Debugging and testing with precise postconditions.
+tags:
+- python
+- testing
+- postconditions
+- sorting
 ---
 
 ## Introduction

ib002/03-time-complexity/extend.md

@@ -2,6 +2,12 @@
 title: Time complexity of ‹extend›
 description: |
   How to make inefficient algorithm unknowingly.
+tags:
+- c
+- python
+- dynamic array
+- time complexity
+- recursion
 ---
 
 ## Introduction

ib002/08-rb-trees/applications.md

@@ -1,8 +1,11 @@
 ---
 title: Použití červeno-černých stromů
 description: |
-  Ukázka použití červeno-černých stromů pro implementaci množiny nebo mapy
-  a ukázky jednotlivých implementací ve standardních knižnicích známých jazyků.
+  Ukázka použití červeno-černých stromů v standardních knižnicích známých jazyků.
+tags:
+- balanced trees
+- red-black trees
+- applications
 ---
 
 ## Použití

ib002/10-graphs/bfs-tree.md

@@ -2,6 +2,9 @@
 title: Distance boundaries from BFS tree on undirected graphs
 description: |
   Short explanation of distance boundaries deduced from a BFS tree.
+tags:
+- graphs
+- bfs
 ---
 
 ## Introduction

ib002/10-graphs/iterative-and-iterators.md

@@ -1,7 +1,12 @@
 ---
 title: Iterative algorithms via iterators
 description: |
-  Examples of iterative implementations of DFS using iterators.
+  Iterative DFS using iterators.
+tags:
+- csharp
+- graphs
+- iterators
+- iterative
 ---
 
 ## Introduction