_content/doc: document -e flag for tidy and vendor

For golang/go#26603

Change-Id: I4bb1138ebda5ded1be30ead19bd6b282eedc3265
Reviewed-on: https://go-review.googlesource.com/c/website/+/287413
Trust: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/_content/doc/mod.md b/_content/doc/mod.md
index c90d2d6..7801c2d 100644
--- a/_content/doc/mod.md
+++ b/_content/doc/mod.md
@@ -1701,7 +1701,7 @@
 Usage:
 
 ```
-go mod tidy [-v]
+go mod tidy [-e] [-v]
 ```
 
 `go mod tidy` ensures that the `go.mod` file matches the source code in the
@@ -1710,6 +1710,9 @@
 don't provide any relevant packages. It also adds any missing entries to
 `go.sum` and removes unnecessary entries.
 
+The `-e` flag (added in Go 1.16) causes `go mod tidy` to attempt to proceed
+despite errors encountered while loading packages.
+
 The `-v` flag causes `go mod tidy` to print information about removed modules
 to standard error.
 
@@ -1746,7 +1749,7 @@
 Usage:
 
 ```
-go mod vendor [-v]
+go mod vendor [-e] [-v]
 ```
 
 The `go mod vendor` command constructs a directory named `vendor` in the [main
@@ -1776,6 +1779,9 @@
 not been modified, but one can verify the integrity of the `vendor` directory
 by running `go mod vendor` and checking that no changes were made.
 
+The `-e` flag (added in Go 1.16) causes `go mod vendor` to attempt to proceed
+despite errors encountered while loading packages.
+
 The `-v` flag causes `go mod vendor` to print the names of vendored modules
 and packages to standard error.