Merge bitcoin-core/secp256k1#1131: readme: Misc improvements

88b0089 readme: Fix line break (Tim Ruffing)
78f5296 readme: Sell "no runtime dependencies" (Tim Ruffing)
ef48f08 readme: Add IRC channel (Tim Ruffing)

Pull request description:

ACKs for top commit:
  apoelstra:
    utACK 88b0089
  sipa:
    ACK 88b0089

Tree-SHA512: 174f1596406f98a19059a18cd4fb993102e5ffb8ec29fcc6d03e27f135fcb526b37204b64055b5e4f0a273daab05d395cf335f26241cf3a29a060041c9ef109b

Author: real-or-random

README.md

@@ -2,6 +2,8 @@ libsecp256k1
 ============
 
 [![Build Status](https://api.cirrus-ci.com/github/bitcoin-core/secp256k1.svg?branch=master)](https://cirrus-ci.com/github/bitcoin-core/secp256k1)
+![Dependencies: None](https://img.shields.io/badge/dependencies-none-success)
+[![irc.libera.chat #secp256k1](https://img.shields.io/badge/irc.libera.chat-%23secp256k1-success)](https://web.libera.chat/#secp256k1)
 
 Optimized C library for ECDSA signatures and secret/public key operations on curve secp256k1.
 
@@ -15,6 +17,7 @@ Features:
 * Derandomized ECDSA (via RFC6979 or with a caller provided function.)
 * Very efficient implementation.
 * Suitable for embedded systems.
+* No runtime dependencies.
 * Optional module for public key recovery.
 * Optional module for ECDH key exchange.
 * Optional module for Schnorr signatures according to [BIP-340](https://github.com/bitcoin/bips/blob/master/bip-0340.mediawiki).
@@ -72,11 +75,12 @@ To compile optional modules (such as Schnorr signatures), you need to run `./con
 
 Usage examples
 -----------
-  Usage examples can be found in the [examples](examples) directory. To compile them you need to configure with `--enable-examples`.
+Usage examples can be found in the [examples](examples) directory. To compile them you need to configure with `--enable-examples`.
   * [ECDSA example](examples/ecdsa.c)
   * [Schnorr signatures example](examples/schnorr.c)
   * [Deriving a shared secret (ECDH) example](examples/ecdh.c)
-  To compile the Schnorr signature and ECDH examples, you also need to configure with `--enable-module-schnorrsig` and `--enable-module-ecdh`.
+
+To compile the Schnorr signature and ECDH examples, you also need to configure with `--enable-module-schnorrsig` and `--enable-module-ecdh`.
 
 Test coverage
 -----------