docs: [#463] system package dep: libssl-dev

Since we are using native TLS support you need to install `libssl-dev`
on Linux:

```
sudo apt-get install libssl-dev
```

project-words.txt

@@ -68,6 +68,7 @@ rowid
 RUSTDOCFLAGS
 RUSTFLAGS
 rustfmt
+rustls
 rustversion
 serde
 sgxj

src/lib.rs

@@ -53,7 +53,7 @@
 //! ## Prerequisites
 //!
 //! In order the run the index you will need a running torrust tracker. In the
-//! configuration you need to fill the `index` section with the following:
+//! configuration you need to fill the `tracker` section with the following:
 //!
 //! ```toml
 //! [tracker]
@@ -69,6 +69,16 @@
 //! You can follow the tracker installation instructions [here](https://docs.rs/torrust-tracker)
 //! or you can use the docker to run both the tracker and the index. Refer to the
 //! [Run with docker](#run-with-docker) section for more information.
+//! 
+//! You will also need to install this dependency:
+//! 
+//! ```text
+//! sudo apt-get install libssl-dev
+//! ```
+//! 
+//! We needed because we are using native TLS support instead of [rustls](https://github.com/rustls/rustls).
+//! 
+//! More info: <https://github.com/torrust/torrust-index/issues/463>.
 //!
 //! If you are using `SQLite3` as database driver, you will need to install the
 //! following dependency: