Fix read the docs build (#820)

* add environment config for conda in readthedocs

* use python confs

* add checking readthedocs to instructions

.readthedocs.yml

@@ -0,0 +1,21 @@
+# .readthedocs.yml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  configuration: doc/conf.py
+
+conda:
+  environment: doc/environment.yml
+
+python:
+  version: 3.7
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - doc
+  system_packages: true

doc/environment.yml

@@ -0,0 +1,5 @@
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - rust

doc/release.md

@@ -1,6 +1,5 @@
 # Releasing a new version of sourmash
 
-
 These are adapted from the khmer release docs, originally written by
 Michael Crusoe.
 
@@ -10,6 +9,9 @@ Remember to update release numbers/RC in:
 
 ## Testing a release
 
+ 0\. First things first: check if Read the Docs is building properly for
+ master. Build on https://readthedocs.org/projects/sourmash/builds/ should be
+ passing, and also check if https://sourmash.readthedocs.io/en/latest/ is updated.
 
  1\. The below should be done in a clean checkout:
 ```
@@ -19,7 +21,7 @@ cd sourmash
 ```
 2\. Set your new version number and release candidate (you might want to check https://github.com/dib-lab/sourmash/releases for next version number):
 ```
-new_version=1.0.0
+new_version=3.0.0
 rc=rc1
 ```
  and then tag the release candidate with the new version number prefixed by