doc, src: Fix various spelling typos

Signed-off-by: Jordan Justen <jljusten@gmail.com>

src/libstore/builtins/unpack-channel.cc

@@ -20,7 +20,7 @@ void builtinUnpackChannel(
     auto & src = getAttr("src");
 
     if (fs::path{channelName}.filename().string() != channelName) {
-        throw Error("channelName is not allowed to contain filesystem seperators, got %1%", channelName);
+        throw Error("channelName is not allowed to contain filesystem separators, got %1%", channelName);
     }
 
     try {

src/libstore/local-overlay-store.md

@@ -4,7 +4,7 @@ R"(
 
 This store type is a variation of the [local store] designed to leverage Linux's [Overlay Filesystem](https://docs.kernel.org/filesystems/overlayfs.html) (OverlayFS for short).
 Just as OverlayFS combines a lower and upper filesystem by treating the upper one as a patch against the lower, the local overlay store combines a lower store with an upper almost-[local store].
-("almost" because while the upper fileystems for OverlayFS is valid on its own, the upper almost-store is not a valid local store on its own because some references will dangle.)
+("almost" because while the upper filesystems for OverlayFS is valid on its own, the upper almost-store is not a valid local store on its own because some references will dangle.)
 To use this store, you will first need to configure an OverlayFS mountpoint [appropriately](#example-filesystem-layout) as Nix will not do this for you (though it will verify the mountpoint is configured correctly).
 
 ### Conceptual parts of a local overlay store

src/libstore/local.mk

@@ -59,7 +59,7 @@ NIX_ROOT =
 endif
 
 # Prefix all but `NIX_STORE_DIR`, since we aren't doing a local store
-# yet so a "logical" store dir that is the same as unix is prefered.
+# yet so a "logical" store dir that is the same as unix is preferred.
 #
 # Also, it keeps the unit tests working.