Split README into separate files (#150)

* Create a separate udp README file

* Split README into separate files for all three implementations

* Minor README fixes

crates/http/README.md

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+# aquatic_http: high-performance open HTTP BitTorrent tracker
+
+[![CI](https://github.com/greatest-ape/aquatic/actions/workflows/ci.yml/badge.svg)](https://github.com/greatest-ape/aquatic/actions/workflows/ci.yml)
+
+High-performance open HTTP BitTorrent tracker for Linux 5.8 or later.
+
+Features at a glance:
+
+- Multithreaded design for handling large amounts of traffic
+- All data is stored in-memory (no database needed)
+- IPv4 and IPv6 support
+- Supports forbidding/allowing info hashes
+- Prometheus metrics
+- Automated CI testing of full file transfers
+
+## Performance
+
+![HTTP BitTorrent tracker throughput comparison](../../documents/aquatic-http-load-test-illustration-2023-01-25.png)
+
+More benchmark details are available [here](../../documents/aquatic-http-load-test-2023-01-25.pdf).
+
+## Usage
+
+### Compiling
+
+- Install Rust with [rustup](https://rustup.rs/) (latest stable release is recommended)
+- Install cmake with your package manager (e.g., `apt-get install cmake`)
+- Clone this git repository and enter its root directory
+- Build the application:
+
+```sh
+# Recommended: tell Rust to enable support for all SIMD extensions present on
+# current CPU except for those relating to AVX-512. (If you run a processor
+# that doesn't clock down when using AVX-512, you can enable those instructions
+# too.)
+. ./scripts/env-native-cpu-without-avx-512
+
+cargo build --release -p aquatic_http
+```
+
+### Configuring
+
+Generate the configuration file:
+
+```sh
+./target/release/aquatic_http -p > "aquatic-http-config.toml"
+```
+
+Make necessary adjustments to the file. You will likely want to adjust `address`
+(listening address) under the `network` section.
+
+`aquatic_http` __only__ runs over TLS, so configuring certificate and private
+key files is required.
+
+Running behind a reverse proxy is currently not supported due to the
+[difficulties of determining the originating IP address](https://adam-p.ca/blog/2022/03/x-forwarded-for/)
+without knowing the exact setup.
+
+### Running
+
+Make sure locked memory limits are sufficient:
+- If you're using a systemd service file, add `LimitMEMLOCK=65536000` to it
+- Otherwise, add the following lines to
+`/etc/security/limits.conf`, and then log out and back in:
+
+```
+*    hard    memlock    65536
+*    soft    memlock    65536
+```
+
+Once done, start the application:
+
+```sh
+./target/release/aquatic_http -c "aquatic-http-config.toml"
+```
+
+If your server is pointed to by domain `example.com` and you configured the
+tracker to run on port 3000, people can now use it by adding the URL
+`https://example.com:3000/announce` to their torrent files or magnet links.
+
+### Load testing
+
+A load test application is available. It supports generation and loading of
+configuration files in a similar manner to the tracker application.
+
+After starting the tracker, run the load tester:
+
+```sh
+./scripts/run-load-test-http.sh
+```
+
+## Details
+
+[BEP 003]: https://www.bittorrent.org/beps/bep_0003.html
+[BEP 007]: https://www.bittorrent.org/beps/bep_0007.html
+[BEP 023]: https://www.bittorrent.org/beps/bep_0023.html
+[BEP 048]: https://www.bittorrent.org/beps/bep_0048.html
+
+Implements:
+  * [BEP 003]: HTTP BitTorrent protocol ([more details](https://wiki.theory.org/index.php/BitTorrentSpecification#Tracker_HTTP.2FHTTPS_Protocol)). Exceptions:
+    * Only runs over TLS
+    * Doesn't track the number of torrent downloads (0 is always sent)
+    * Only compact responses are supported
+  * [BEP 023]: Compact HTTP responses
+  * [BEP 007]: IPv6 support
+  * [BEP 048]: HTTP scrape support. Notes:
+    * Doesn't allow full scrapes, i.e. of all registered info hashes
+
+`aquatic_http` has not been tested as much as `aquatic_udp`, but likely works
+fine in production.
+
+## Copyright and license
+
+Copyright (c) 2020-2023 Joakim Frostegård
+
+Distributed under the terms of the Apache 2.0 license. Please refer to the
+`LICENSE` file in the repository root directory for details.