README.md: QEMU no longer needs to be signed manually

The latest homebrew package seems signed by default.

```console
$ codesign -d --entitlements :- /usr/local/Cellar/qemu/6.0.0/bin/qemu-system-x86_64
Executable=/usr/local/Cellar/qemu/6.0.0/bin/qemu-system-x86_64
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>com.apple.security.hypervisor</key>
    <true/>
</dict>
</plist>
```

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

README.md

@@ -75,9 +75,19 @@ For the usage of containerd and nerdctl (contaiNERD ctl), visit https://github.c
 
 ## Getting started
 ### Requirements (Intel Mac)
-- QEMU (`brew install qemu`)
+- QEMU v6.0.0 or later (`brew install qemu`)
 
-- Run the following commands to enable `--accel=hvf`:
+
+<details>
+<summary>
+Signing the binary (not needed for recent version of QEMU and macOS, in most cases)
+</summary>
+
+<p>
+
+If you have installed QEMU v6.0.0 or later on macOS 11, your binary should have been already automatically signed to enable HVF acceleration.
+
+However, if you see `HV_ERROR`, you might need to sign the binary manually.
 
 ```bash
 cat >entitlements.xml <<EOF
@@ -101,6 +111,8 @@ Note: **Only** on macOS versions **before** 10.15.7 you might need to add this e
     <true/>
 ```
 
+</p>
+</details>
 
 ### Requirements (ARM Mac)