Add task desctiption for each day

day-05/README.md

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+# Day 5: Hydrothermal Venture
+
+[https://adventofcode.com/2021/day/5](https://adventofcode.com/2021/day/5)
+
+## Description
+
+### Part One
+
+You come across a field of [hydrothermal vents](https://en.wikipedia.org/wiki/Hydrothermal_vent) on the ocean floor! These vents constantly produce large, opaque clouds, so it would be best to avoid them if possible.
+
+They tend to form in _lines_; the submarine helpfully produces a list of nearby <span title="Maybe they're Bresenham vents.">lines of vents</span> (your puzzle input) for you to review. For example:
+
+    0,9 -> 5,9
+    8,0 -> 0,8
+    9,4 -> 3,4
+    2,2 -> 2,1
+    7,0 -> 7,4
+    6,4 -> 2,0
+    0,9 -> 2,9
+    3,4 -> 1,4
+    0,0 -> 8,8
+    5,5 -> 8,2
+    
+
+Each line of vents is given as a line segment in the format `x1,y1 -> x2,y2` where `x1`,`y1` are the coordinates of one end the line segment and `x2`,`y2` are the coordinates of the other end. These line segments include the points at both ends. In other words:
+
+*   An entry like `1,1 -> 1,3` covers points `1,1`, `1,2`, and `1,3`.
+*   An entry like `9,7 -> 7,7` covers points `9,7`, `8,7`, and `7,7`.
+
+For now, _only consider horizontal and vertical lines_: lines where either `x1 = x2` or `y1 = y2`.
+
+So, the horizontal and vertical lines from the above list would produce the following diagram:
+
+    .......1..
+    ..1....1..
+    ..1....1..
+    .......1..
+    .112111211
+    ..........
+    ..........
+    ..........
+    ..........
+    222111....
+    
+
+In this diagram, the top left corner is `0,0` and the bottom right corner is `9,9`. Each position is shown as _the number of lines which cover that point_ or `.` if no line covers that point. The top-left pair of `1`s, for example, comes from `2,2 -> 2,1`; the very bottom row is formed by the overlapping lines `0,9 -> 5,9` and `0,9 -> 2,9`.
+
+To avoid the most dangerous areas, you need to determine _the number of points where at least two lines overlap_. In the above example, this is anywhere in the diagram with a `2` or larger - a total of _`5`_ points.
+
+Consider only horizontal and vertical lines. _At how many points do at least two lines overlap?_
+
+### Part Two
+
+Unfortunately, considering only horizontal and vertical lines doesn't give you the full picture; you need to also consider _diagonal lines_.
+
+Because of the limits of the hydrothermal vent mapping system, the lines in your list will only ever be horizontal, vertical, or a diagonal line at exactly 45 degrees. In other words:
+
+*   An entry like `1,1 -> 3,3` covers points `1,1`, `2,2`, and `3,3`.
+*   An entry like `9,7 -> 7,9` covers points `9,7`, `8,8`, and `7,9`.
+
+Considering all lines from the above example would now produce the following diagram:
+
+    1.1....11.
+    .111...2..
+    ..2.1.111.
+    ...1.2.2..
+    .112313211
+    ...1.2....
+    ..1...1...
+    .1.....1..
+    1.......1.
+    222111....
+    
+
+You still need to determine _the number of points where at least two lines overlap_. In the above example, this is still anywhere in the diagram with a `2` or larger - now a total of _`12`_ points.
+
+Consider all of the lines. _At how many points do at least two lines overlap?_