add CRAN comments for v0.5.0 release

.Rbuildignore

@@ -10,3 +10,4 @@ dev$
 ^appveyor\.yml$
 ^codecov\.yml$
 ^CRAN-RELEASE$
+^cran-comments\.md$

cran-comments.md

@@ -0,0 +1,26 @@
+## Submission info
+
+Several feature updates.
+
+## Test environments
+
+* Windows 10 (local desktop), R 4.0.3
+* Ubuntu 16.04.6 LTS (travis-ci), R 4.0.3
+* Windows Server x64 (appveyor.com) R 4.0.3
+* win-builder (devel and release)
+* R-hub builder
+
+## R CMD check results
+
+0 errors | 0 warnings | 1 notes
+
+  Imports includes 24 non-default packages.
+  Importing from so many packages makes the package vulnerable to any of
+  them becoming unavailable.  Move as many as possible to Suggests and
+  use conditionally.
+
+   => THIS IS OKAY FOR US
+
+## Reverse dependencies
+
+There are no reverse dependencies.