Add subject for the exercise `commits_stats`

subjects/commits_stats/README.md

@@ -0,0 +1,58 @@
+## commit_stats
+
+### Instructions:
+
+In this exercise you will be provided with a json file `commits.json` with data corresponding to git commits in GitHub (extracted using the GitHub rest API), your job is to extract the relevant data and place it in a struct called `CommitData` to get the following information:
+
+1. Number of commits per author (identified by the GitHub login).
+
+2. The number of commits per author.
+
+Create two functions:
+
+- `commits_per_author`: which returns a hash map with the number of commits per author.
+
+- `commits_per_date`: which returns a hash map with the number of commits per week.
+
+  - Note: A week is represented by the a year followed by the number of the
+week for example January 1, 2020 is in week 1 of 2020 an will be
+represented by a String with the form "2020-W1".
+
+### Notions:
+
+- [chrono](https://docs.rs/chrono/0.4.19/chrono)
+- [json](https://docs.rs/json/0.12.4/json/index.html)
+
+### Expected functions
+
+```rust
+pub fn commits_per_week(data: &json::JsonValue) -> HashMap<String, u32> {
+}
+
+pub fn commits_per_author(data: &json::JsonValue) -> HashMap<String, u32> {
+}
+```
+
+### Usage
+
+Here is a possible test for your function:
+
+```rust
+use commit_stats::{commits_per_week, commits_per_author};
+
+fn main() {
+	let contents = fs::read_to_string("commits.json").unwrap();
+	let serialized = json::parse(&contents).unwrap();
+	println!("{:?}", commits_per_week(&serialized));
+	println!("{:?}", commits_per_author(&serialized));
+}
+```
+
+And its output:
+
+```console
+student@ubuntu:~/[[ROOT]]/test$ cargo run
+{"2020-W44": 5, "2020-W36": 1, "2020-W31": 1, ... ,"2020-W45": 4, "2020-W46": 4}
+{"homembaixinho": 2, "mwenzkowski": 3, ... ,"tamirzb": 1, "paul-ri": 2, "RPigott": 1}
+student@ubuntu:~/[[ROOT]]/test$
+```