Add pcntl and grpc docs (#95)

* Requirements: document PCNTL as a recommended PHP extension

* Requirements: add warning about gRPC extension and parallel processing

The gRPC PHP extension is known to cause PHP_CodeSniffer to hang
when running with parallel processing enabled.

Includes details on how to handle the gRPC extension.

Refs: PHPCSStandards/PHP_CodeSniffer#294

* Spellcheck: also ignore code blocks inside blockquotes

The existing regex pattern for ignoring code blocks only matched
blocks at the start of a line (with optional whitespace). This
update makes it also match code blocks inside markdown
blockquotes, where lines are prefixed with `>`.

Author: rodrigoprimo

.cspell.yml

@@ -12,9 +12,9 @@ patterns:
   - name: markdown_code_block
     pattern: |
       /
-          ^(\s*`{3,})[a-z]+   # match the ``` with a language modifier
-          [\s\S]*?            # the block of code
-          ^\1                 # end of the block
+          ^([\s>]*`{3,})[a-z]+  # match the ``` with a language modifier, optionally inside a blockquote
+          [\s\S]*?              # the block of code
+          ^\1                   # end of the block
       /gmx
   - name: markdown_inline_code
     pattern: /(\s*`)[^`\n]{3,}`/gmx

wiki/Requirements.md

@@ -6,7 +6,14 @@ Additionally, PHP_CodeSniffer requires the following PHP extensions to be enable
 - SimpleXML: used to process ruleset XML files
 - XMLWriter: used to create some report formats
 
-The following PHP extension is not required, but is strongly recommended:
+The following PHP extensions are not required, but are strongly recommended:
 - iconv: used for accurate character length calculation in files containing multibyte characters. Without this extension, some sniffs, like `Generic.Files.LineLength`, may report incorrect results for lines containing non-ASCII characters, as PHP_CodeSniffer will fall back to byte-based length calculations.
+- PCNTL: required for parallel processing via the `--parallel` CLI option. Without this extension, PHP_CodeSniffer will not be able to check multiple files simultaneously.
 
 Individual sniffs may have additional requirements such as external applications and scripts. See the [Configuration Options](https://github.com/PHPCSStandards/PHP_CodeSniffer/wiki/Configuration-Options) manual page for a list of these requirements.
+
+> [!WARNING]
+> The gRPC PHP extension is known to cause PHP_CodeSniffer to hang when running with parallel processing enabled. If the gRPC extension is loaded, either do not use the `--parallel` CLI option or configure the extension's ini settings as follows:
+> ```text
+> phpcs -d grpc.enable_fork_support=1 -d grpc.poll_strategy=epoll1 [other options] <file|directory>
+> ```