Create README for certificates setup

Add instructions for generating local pem files using mkcert.

Signed-off-by: Pablo Mayrgundter <pablo.mayrgundter@gmail.com>

Author: pablo-mayrgundter

tools/esbuild/certificates/README.md

@@ -0,0 +1,20 @@
+For https serving, generate local pem files and put them in this directory.
+
+# Using mkcert on OSX
+
+```
+# Initially
+
+# Install mkcert if you don't have it
+brew install mkcert
+
+# One-time system install to allow Start of Authority from OS locally
+mkcert -install
+
+# Generate localhost-key.pem and localhost.pem
+mkcert localhost 127.0.0.1 ::1
+```
+
+Note the actual filenames created, and edit the `./proxy.js` hardcoded filenames to match them exactly.
+
+After this, running our https targets should work fine.