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/command-ref/nix-store/generate-binary-cache-key.md

@@ -0,0 +1,29 @@
+# Name
+
+`nix-store --generate-binary-cache-key` - generate key pair to use for a binary cache
+
+## Synopsis
+
+`nix-store` `--generate-binary-cache-key` *key-name* *secret-key-file* *public-key-file*
+
+## Description
+
+This command generates an [Ed25519 key pair](http://ed25519.cr.yp.to/)
+that can be used to create a signed binary cache. It takes three
+mandatory parameters:
+
+1.  A key name, such as `cache.example.org-1`, that is used to look up
+    keys on the client when it verifies signatures. It can be anything,
+    but it’s suggested to use the host name of your cache (e.g.
+    `cache.example.org`) with a suffix denoting the number of the key
+    (to be incremented every time you need to revoke a key).
+
+2.  The file name where the secret key is to be stored.
+
+3.  The file name where the public key is to be stored.
+
+{{#include ./opt-common.md}}
+
+{{#include ../opt-common.md}}
+
+{{#include ../env-common.md}}