Point links at the moved documents and config example

ARCHITECTURE.md, TODO.md and config.example.yml moved to docs/ and
configs/ on next. README.md now links to the new paths. docs/ARCHITECTURE.md
and the roadmap in docs/TODO.md link to their sibling documents by file
name, as docs/DATAMODEL.md and docs/REPOSTRUCTURE.md already do. The help
text and configs/config.example.yml name none of the old paths.

Model: fable-5-1

docs/ARCHITECTURE.md

@@ -9,8 +9,8 @@ things:
 
 Two other documents cover the stored data:
 
-- [`docs/DATAMODEL.md`](docs/DATAMODEL.md) describes the local index.
-- [`docs/REPOSTRUCTURE.md`](docs/REPOSTRUCTURE.md) describes the layout of the
+- [`DATAMODEL.md`](DATAMODEL.md) describes the local index.
+- [`REPOSTRUCTURE.md`](REPOSTRUCTURE.md) describes the layout of the
   destination.
 
 ## Terms
@@ -59,9 +59,8 @@ source files
 - `internal/blobgen`: the writer that hashes, compresses and encrypts a blob,
   and the reader that reverses it.
 - `internal/database`: the local index. It holds the schema and the repository
-  types that read and write the tables.
-  [`docs/DATAMODEL.md`](docs/DATAMODEL.md#code) says which type serves which
-  table.
+  types that read and write the tables. [`DATAMODEL.md`](DATAMODEL.md#code) says
+  which type serves which table.
 - `internal/storage`: the `Storer` interface and its three implementations, for
   S3, a local directory and [rclone](https://rclone.org/).
 - `internal/s3`: the S3 client that the S3 `Storer` uses.
@@ -231,8 +230,7 @@ chunker buffers at most twice the largest chunk size.
 
 The blob's name is `hex(SHA256(SHA256(uncompressed contents)))`. It is computed
 from the chunk data before compression and encryption.
-[`docs/REPOSTRUCTURE.md`](docs/REPOSTRUCTURE.md#blobs) says what follows from
-that.
+[`REPOSTRUCTURE.md`](REPOSTRUCTURE.md#blobs) says what follows from that.
 
 When a blob is closed, `Scanner.handleBlobReady` stores it:
 
@@ -362,8 +360,8 @@ of object, once they are older than `prune_grace_period`:
   in the local index
 
 It deletes nothing when any manifest cannot be read.
-[`docs/REPOSTRUCTURE.md`](docs/REPOSTRUCTURE.md#pruning) explains why this is
-safe, and where it is not.
+[`REPOSTRUCTURE.md`](REPOSTRUCTURE.md#pruning) explains why this is safe, and
+where it is not.
 
 ## The destination