Update certificate environment variable advice for pantsbuild#14808. (p…

…antsbuild#15943)

See pantsbuild#14808.

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docs/markdown/Using Pants/restricted-internet-access.md

@@ -24,7 +24,9 @@ You may want to check the binary into version control so that everyone in your o
 Setting up a Certificate Authority
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-You may need to configure Pants to use a custom Certificate Authority (CA) bundle: 
+By default, Pants will respect and pass through the `SSL_CERT_DIR` and `SSL_CERT_FILE` environment variables.
+
+If you need to override those values, you can configure Pants to use a custom Certificate Authority (CA) bundle:
 
 ```toml pants.toml
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