Update guides/hack from HHVM repository

Author: Wilfred

guides/hack/18-packages/01-introduction.md

@@ -71,6 +71,14 @@ When determining which package a file belongs to:
 3. Otherwise, the file belongs to the package whose `include_paths` contains the file's nearest ancestor directory (i.e. the longest prefix match)
 4. If none of the above apply, the file belongs to the **default package**
 
+### Manual Global Exclusions
+
+It is possible globally exclude files from deployements and/or typechecking. This is controlled for the build by `exclude-pattern` build_config.hdf and for the typechecker by `package_exclude_patterns` in .hhconfig.
+- They are excluded from the typechecker (no errors are reported for references to or from these files)
+- They are automatically excluded from all deployments, regardless of package membership
+
+By default, that includes files whose path contains the substring `__tests__`.
+
 ## Default package
 
 Any file not specified in any package (neither via `include_paths` nor `__PackageOverride`) belongs to the implicit "default" package. Symbols within the default package are not accessible from other packages. The default package:

guides/hack/18-packages/02-deployments.md

@@ -67,6 +67,7 @@ Eval.Runtime.ActiveDeployment = production
 
 When running in [repo authoritative](/docs/hhvm/advanced-usage/repo-authoritative) mode, HHVM only compiles and runs files from packages in the specified deployment. References to undeployed packages cause runtime errors (e.g., "Class not found" or "Call to undefined function"). When running in other modes, the active deployment serves only to modify semantics of `package` checks and the `__RequirePackage` attribute.
 
+**Note:** Files in `__tests__` directories are automatically excluded from all deployments. See [File package membership](/docs/hack/packages/introduction#test-directories) for details.
 
 ### Force Symbol References (Legacy)