docs: add a section for the -compress flag (vlang#22169)

doc/docs.md

@@ -6725,15 +6725,16 @@ performance, memory usage, or size.
 
 | Tuning Operation         | Benefits                        | Drawbacks                                         |
 |--------------------------|---------------------------------|---------------------------------------------------|
-| `@[inline]`               | Performance                     | Increased executable size                         |
-| `@[direct_array_access]`  | Performance                     | Safety risks                                      |
-| `@[packed]`               | Memory usage                    | Potential performance loss                        |
-| `@[minify]`               | Performance, Memory usage       | May break binary serialization/reflection         |
+| `@[inline]`              | Performance                     | Increased executable size                         |
+| `@[direct_array_access]` | Performance                     | Safety risks                                      |
+| `@[packed]`              | Memory usage                    | Potential performance loss                        |
+| `@[minify]`              | Performance, Memory usage       | May break binary serialization/reflection         |
 | `_likely_/_unlikely_`    | Performance                     | Risk of negative performance impact               |
 | `-skip-unused`           | Performance, Compile time, Size | Potential instability                             |
 | `-fast-math`             | Performance                     | Risk of incorrect mathematical operations results |
 | `-d no_segfault_handler` | Compile time, Size              | Loss of segfault trace                            |
 | `-cflags -march=native`  | Performance                     | Risk of reduced CPU compatibility                 |
+| `-compress`              | Size                            | Harder to debug, extra dependency `upx`           |
 | `PGO`                    | Performance, Size               | Usage complexity                                  |
 
 ### Tuning operations details
@@ -6920,6 +6921,22 @@ with identical hardware.
 
 - When distributing the software to users with potentially older CPUs.
 
+#### `-compress`
+
+This flag executes `upx` to compress the resultant executable,
+reducing its size by around 50%-70%.
+
+**When to Use**
+
+- For really tiny environments, where the size of the executable on the file system,
+or when deploying is important. The executable will be uncompressed at runtime,
+so it will take a bit more time to start.
+
+**When to Avoid**
+
+- When you need to debug the application, or when your app's startup time
+is extremely important (where 1-2ms can be meaningful for you).
+
 #### PGO (Profile-Guided Optimization)
 
 PGO allows the compiler to optimize code based on its behavior during sample runs. This can improve