title: Rtools not found by R when installing packages from CRAN
body: <p>When install any new package I get errors saying Rtools is not found. I followed the manual install instructions for Rtools but still get the same error message.</p>
  
  <pre><code>&gt; install.packages("phyloseq")
  WARNING: Rtools is required to build R packages but is not currently installed. Please download and install the appropriate version of Rtools before proceeding
  </code></pre>
  
  <p>It seems R is not finding Rtools. Is there anyway to fix this?</p>
  
  <p>I have noticed a second issue of previously installed packages disappearing also when starting new R sessions. Could these two issues be linked?</p>
  
  <p>My R version in 4.0 and I am working in Windows 64bit</p>