Rename doc/manual{src -> source}

This is needed to avoid this
https://github.com/mesonbuild/meson/issues/13774 when we go back to
making our subproject directory `src`.

doc/manual/source/release-notes/rl-1.4.md

@@ -0,0 +1,22 @@
+# Release 1.4 (2013-02-26)
+
+This release fixes a security bug in multi-user operation. It was
+possible for derivations to cause the mode of files outside of the Nix
+store to be changed to 444 (read-only but world-readable) by creating
+hard links to those files
+([details](https://github.com/NixOS/nix/commit/5526a282b5b44e9296e61e07d7d2626a79141ac4)).
+
+There are also the following improvements:
+
+  - New built-in function: `builtins.hashString`.
+
+  - Build logs are now stored in `/nix/var/log/nix/drvs/XX/`, where *XX*
+    is the first two characters of the derivation. This is useful on
+    machines that keep a lot of build logs (such as Hydra servers).
+
+  - The function `corepkgs/fetchurl` can now make the downloaded file
+    executable. This will allow getting rid of all bootstrap binaries in
+    the Nixpkgs source tree.
+
+  - Language change: The expression `"${./path}
+            ..."` now evaluates to a string instead of a path.