instrumenting: add process_virtual_memory_max_bytes

Signed-off-by: Simon Pasquier <spasquie@redhat.com>

content/docs/instrumenting/writing_clientlibs.md

@@ -333,15 +333,16 @@ These exports should have the prefix `process_`. If a language or runtime
 doesn't expose one of the variables it'd just not export it. All memory values
 in bytes, all times in unixtime/seconds.
 
-| Metric name                     | Help string                                            | Unit             |
-| ------------------------------- | ------------------------------------------------------ | ---------------  |
-| `process_cpu_seconds_total`     | Total user and system CPU time spent in seconds.       | seconds          |
-| `process_open_fds`              | Number of open file descriptors.                       | file descriptors |
-| `process_max_fds`               | Maximum number of open file descriptors.               | file descriptors |
-| `process_virtual_memory_bytes`  | Virtual memory size in bytes.                          | bytes            |
-| `process_resident_memory_bytes` | Resident memory size in bytes.                         | bytes            |
-| `process_heap_bytes`            | Process heap size in bytes.                            | bytes            |
-| `process_start_time_seconds`    | Start time of the process since unix epoch in seconds. | seconds          |
+| Metric name                        | Help string                                            | Unit             |
+| ---------------------------------- | ------------------------------------------------------ | ---------------  |
+| `process_cpu_seconds_total`        | Total user and system CPU time spent in seconds.       | seconds          |
+| `process_open_fds`                 | Number of open file descriptors.                       | file descriptors |
+| `process_max_fds`                  | Maximum number of open file descriptors.               | file descriptors |
+| `process_virtual_memory_bytes`     | Virtual memory size in bytes.                          | bytes            |
+| `process_virtual_memory_max_bytes` | Maximum amount of virtual memory available in bytes.   | bytes            |
+| `process_resident_memory_bytes`    | Resident memory size in bytes.                         | bytes            |
+| `process_heap_bytes`               | Process heap size in bytes.                            | bytes            |
+| `process_start_time_seconds`       | Start time of the process since unix epoch in seconds. | seconds          |
 
 ### Runtime metrics