NFC: Fix typos in PackageLoading (#2977)

The sentence in the second paragraph of `README.md` is unfinished. I'm not sure how it was supposed to look originally, so just cleaning it up as is.

Author: MaxDesiatov

Sources/PackageLoading/README.md

@@ -4,7 +4,7 @@ This library defines the logic which translates between the Swift package
 manager conventions and the underlying project model.
 
 The intent is that it is largely a transformation taking the input project model
-objects descripted in a manifest, applying the conventions and
+objects descripted in a manifest applying the conventions.
 
 Ultimately, this library should *only* deal with the content which is _local_ to
 a single package. Any cross-package information should be managed by the

Sources/PackageLoading/TargetSourcesBuilder.swift

@@ -13,7 +13,7 @@ import TSCBasic
 import PackageModel
 import TSCUtility
 
-/// An utility to compute the source/resource files of a target.
+/// A utility to compute the source/resource files of a target.
 public struct TargetSourcesBuilder {
     /// The target for which we're computing source/resource files.
     public let target: TargetDescription