Add note about backward-slashes

Fixes #93

index.d.ts

@@ -40,6 +40,8 @@ declare const del: {
 	/**
 	Delete files and directories using glob patterns.
 
+	Note that glob patterns can only contain forward-slashes, not backward-slashes, so if you want to construct a glob pattern from path components, you need to use `path.posix.join()` instead of `path.join()`.
+
 	@param patterns - See the supported [glob patterns](https://github.com/sindresorhus/globby#globbing-patterns).
 	- [Pattern examples with expected matches](https://github.com/sindresorhus/multimatch/blob/master/test/test.js)
 	- [Quick globbing pattern overview](https://github.com/sindresorhus/multimatch#globbing-patterns)
@@ -65,6 +67,8 @@ declare const del: {
 	/**
 	Synchronously delete files and directories using glob patterns.
 
+	Note that glob patterns can only contain forward-slashes, not backward-slashes, so if you want to construct a glob pattern from path components, you need to use `path.posix.join()` instead of `path.join()`.
+
 	@param patterns - See the supported [glob patterns](https://github.com/sindresorhus/globby#globbing-patterns).
 	- [Pattern examples with expected matches](https://github.com/sindresorhus/multimatch/blob/master/test/test.js)
 	- [Quick globbing pattern overview](https://github.com/sindresorhus/multimatch#globbing-patterns)

readme.md

@@ -46,6 +46,8 @@ Suggestions on how to improve this welcome!
 
 ## API
 
+Note that glob patterns can only contain forward-slashes, not backward-slashes, so if you want to construct a glob pattern from path components, you need to use `path.posix.join()` instead of `path.join()`.
+
 ### del(patterns, options?)
 
 Returns `Promise<string[]>` with the deleted paths.