Depend on specific commit of Guix upstream.

* .guix-channel: Depend on specific commit of Guix upstream.
* README.org: Update recommended channels.scm and explain dependence
on specific commit.

.guix-channel

@@ -8,4 +8,14 @@
     (make-channel-introduction
      "0c119db2ea86a389769f4d2b9c6f5c41c027e336"
      (openpgp-fingerprint
-      "3CE4 6455 8A84 FDC6 9DB4  0CFB 090B 1199 3D9A EBB5"))))))
+      "3CE4 6455 8A84 FDC6 9DB4  0CFB 090B 1199 3D9A EBB5"))))
+  (channel
+   (name guix)
+   (url "https://git.savannah.gnu.org/git/guix.git")
+   (branch "master")
+   (commit "f1ec2d676df9822c3b74acf236f96011784a8642")
+   (introduction
+    (make-channel-introduction
+     "9edb3f66fd807b096b48283debdcddccfea34bad"
+     (openpgp-fingerprint
+      "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA"))))))

README.org

@@ -16,17 +16,18 @@ To easily use the packages from this repo, simply add it to your
 [[https://guix.gnu.org/manual/en/html_node/Channels.html][here]]:
 
 #+BEGIN_SRC scheme
-    (cons*
-      (channel
-        (name 'gn-bioinformatics)
-        (url "https://git.genenetwork.org/guix-bioinformatics/guix-bioinformatics.git")
-        (branch "master"))
-      %default-channels)
+  (list (channel
+         (name 'gn-bioinformatics)
+         (url "https://git.genenetwork.org/guix-bioinformatics/guix-bioinformatics.git")
+         (branch "master")))
 #+END_SRC
 
-and run `guix pull` like normal to update your software. This is the
+and run /guix pull/ like normal to update your software. This is the
 recommended way to use the software from this repository and the code
-snippets in this README assume you have done so.
+snippets in this README assume you have done so. In order to maintain
+stability, the guix-bioinformatics channel depends on a specific
+commit of upstream Guix. So, it is recommended to isolate use of the
+guix-bioinformatics channel in a separate /guix pull/ profile.
 
 If you want to make changes to the packages in this repo then simply set
 the GUIX_PACKAGE_PATH to point to the root of this directory