docs(faq): Include an entry on disk space (#16349)

### What does this PR try to resolve?

Seen a lot of threads where people are asking this question so I figured
it would help if we had an official answer.

Example:
https://www.reddit.com/r/rust/comments/1perari/pain_point_of_rust/nseoj9p/

### How to test and review this PR?

Author: weihanglo

src/doc/src/CHANGELOG.md

@@ -2964,7 +2964,7 @@
   - These settings can be configured in `[registry]` and `[registries]` tables.
 - 🎉 `--keep-going` flag has been stabilized and is now available in each build command
   (except `bench` and `test`, which have `--no-fail-fast` instead).
-  ([docs](https://doc.rust-lang.org/cargo/commands/cargo-build.html#option-cargo-build---keep-going))
+  ([docs](commands/cargo-build.md#option-cargo-build---keep-going))
   [#12568](https://github.com/rust-lang/cargo/pull/12568)
 - Added `--dry-run` flag and summary line at the end for `cargo clean`.
   [#12638](https://github.com/rust-lang/cargo/pull/12638)
@@ -4130,7 +4130,7 @@
 ### Fixed
 - 🚨 [CVE-2022-46176](https://github.com/rust-lang/cargo/security/advisories/GHSA-r5w3-xm58-jv6j):
   Added validation of SSH host keys for git URLs.
-  See [the docs](https://doc.rust-lang.org/cargo/appendix/git-authentication.html#ssh-known-hosts) for more information on how to configure the known host keys.
+  See [the docs](appendix/git-authentication.md#ssh-known-hosts) for more information on how to configure the known host keys.
 
 ## Cargo 1.66 (2022-12-15)
 [08250398...rust-1.66.0](https://github.com/rust-lang/cargo/compare/08250398...rust-1.66.0)
@@ -6912,7 +6912,7 @@
 ### Added
 - Registries may now display warnings after a successful publish.
   [#6303](https://github.com/rust-lang/cargo/pull/6303)
-- Added a [glossary](https://doc.rust-lang.org/cargo/appendix/glossary.html)
+- Added a [glossary](appendix/glossary.md)
   to the documentation. [#6321](https://github.com/rust-lang/cargo/pull/6321)
 - Added the alias `c` for `cargo check`.
   [#6218](https://github.com/rust-lang/cargo/pull/6218)

src/doc/src/faq.md

@@ -290,7 +290,20 @@ causes and provide diagnostic techniques to help you out there:
   and `Cargo.toml` using a [custom merge tool].
 
 
-[links]: https://doc.rust-lang.org/cargo/reference/resolver.html#links
-[conventions in place]: https://doc.rust-lang.org/cargo/reference/build-scripts.html#-sys-packages
+[links]: reference/resolver.md#links
+[conventions in place]: reference/build-scripts.md#-sys-packages
 [`direct-minimal-versions`]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#direct-minimal-versions
 [custom merge tool]: https://github.com/rust-lang/cargo/issues/1818
+
+## Why does my build take up so much space?
+
+Cargo trades off disk space for faster builds including:
+- Maintaining a [cache] of intermediate build artifacts to avoid rebuilding everything when making changes to one package
+- Maintaining distinct [cache] entries for different combinations of toolchain versions, package versions, features, etc to avoid rebuilding packages when switching back and forth between configurations
+- Enabling [incremental compilation] for local packages for faster rebuilds for the package that changed
+- Enabling [debuginfo] in the [`dev` profile] in case you use a debugger
+
+[incremental compilation]: reference/profiles.md#incremental
+[debuginfo]: reference/profiles.md#debug
+[`dev` profile]: reference/profiles.md#dev
+[cache]: reference/build-cache.md

src/doc/src/reference/semver.md

@@ -2033,8 +2033,8 @@ Mitigation strategies:
   mechanism for new features. These are currently unstable and only available
   in the nightly channel.
 
-[select older versions of your package]: https://doc.rust-lang.org/cargo/reference/resolver.html#rust-version
-[support expectations]: https://doc.rust-lang.org/cargo/reference/rust-version.html#support-expectations
+[select older versions of your package]: resolver.md#rust-version
+[support expectations]: rust-version.md#support-expectations
 
 ### Possibly-breaking: changing the platform and environment requirements {#env-change-requirements}
 
@@ -2303,7 +2303,7 @@ document what your commitments are.
 
 [`cfg` attribute]: ../../reference/conditional-compilation.md#the-cfg-attribute
 [`no_std`]: ../../reference/names/preludes.html#the-no_std-attribute
-[`package.rust-version`]: https://doc.rust-lang.org/cargo/reference/rust-version.html
+[`package.rust-version`]: rust-version.md
 [`pub use`]: ../../reference/items/use-declarations.html
 [Cargo feature]: features.md
 [Cargo features]: features.md

src/doc/src/reference/source-replacement.md

@@ -110,7 +110,7 @@ registry = "https://example.com/path/to/index"
 
 [protocols]: registries.md#registry-protocols
 
-[crates.io index]: https://doc.rust-lang.org/cargo/reference/registry-index.html
+[crates.io index]: registry-index.md
 
 ## Local Registry Sources