docs(user-guide): update environment-variables

Author: rami3l

doc/user-guide/src/environment-variables.md

@@ -1,45 +1,47 @@
 # Environment variables
 
-- `RUSTUP_HOME` (default: `~/.rustup` or `%USERPROFILE%/.rustup`) Sets the
+- `RUSTUP_HOME` (default: `~/.rustup` or `%USERPROFILE%/.rustup`). Sets the
   root `rustup` folder, used for storing installed toolchains and
   configuration options.
 
-- `RUSTUP_TOOLCHAIN` (default: none) If set, will [override] the toolchain used
+- `RUSTUP_TOOLCHAIN` (default: none). If set, will [override] the toolchain used
   for all rust tool invocations. A toolchain with this name should be installed,
   or invocations will fail. This can specify custom toolchains, installable
   toolchains, or the absolute path to a toolchain.
 
-- `RUSTUP_DIST_SERVER` (default: `https://static.rust-lang.org`) Sets the root
+- `RUSTUP_DIST_SERVER` (default: `https://static.rust-lang.org`). Sets the root
   URL for downloading static resources related to Rust. You can change this to
   instead use a local mirror, or to test the binaries from the staging
   directory.
 
-- `RUSTUP_DIST_ROOT` (default: `https://static.rust-lang.org/dist`)
-  Deprecated. Use `RUSTUP_DIST_SERVER` instead.
+- ~~`RUSTUP_DIST_ROOT`~~ *deprecated* (default: `https://static.rust-lang.org/dist`).
+  Use `RUSTUP_DIST_SERVER` instead.
 
-- `RUSTUP_UPDATE_ROOT` (default `https://static.rust-lang.org/rustup`) Sets
+- `RUSTUP_UPDATE_ROOT` (default `https://static.rust-lang.org/rustup`). Sets
   the root URL for downloading self-update.
 
 - `RUSTUP_IO_THREADS` *unstable* (defaults to reported cpu count). Sets the
   number of threads to perform close IO in. Set to `1` to force
   single-threaded IO for troubleshooting, or an arbitrary number to override
   automatic detection.
 
-- `RUSTUP_TRACE_DIR` *unstable* (default: no tracing) Enables tracing and
+- `RUSTUP_TRACE_DIR` *unstable* (default: no tracing). Enables tracing and
   determines the directory that traces will be written too. Traces are of the
   form PID.trace. Traces can be read by the Catapult project [tracing viewer].
 
-- `RUSTUP_TERM_COLOR` (default: `auto`) Controls whether colored output is used in the terminal.
+- `RUSTUP_DEBUG` *unstable*. When set, enables rustup's debug logging.
+
+- `RUSTUP_TERM_COLOR` (default: `auto`). Controls whether colored output is used in the terminal.
   Set to `auto` to use colors only in tty streams, to `always` to always enable colors,
   or to `never` to disable colors.
 
-- `RUSTUP_UNPACK_RAM` *unstable* (default free memory or 500MiB if unable to tell, min 210MiB) Caps the amount of
+- `RUSTUP_UNPACK_RAM` *unstable* (default free memory or 500MiB if unable to tell, min 210MiB). Caps the amount of
   RAM `rustup` will use for IO tasks while unpacking.
 
-- `RUSTUP_NO_BACKTRACE` Disables backtraces on non-panic errors even when
+- `RUSTUP_NO_BACKTRACE`. Disables backtraces on non-panic errors even when
   `RUST_BACKTRACE` is set.
 
-- `RUSTUP_PERMIT_COPY_RENAME` *unstable* When set, allows rustup to fall-back
+- `RUSTUP_PERMIT_COPY_RENAME` *unstable*. When set, allows rustup to fall-back
   to copying files if attempts to `rename` result in cross-device link
   errors. These errors occur on OverlayFS, which is used by [Docker][dc]. This
   feature sacrifices some transactions protections and may be removed at any