cmd/govulncheck: correct section headers

pkgsite renders headings with "# " prefix as is:
https://pkg.go.dev/golang.org/x/vuln/cmd/govulncheck

Change-Id: I6873cfb48c5e8f229b27b05435d6711c2f666706
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/408174
Run-TryBot: Zvonimir Pavlinovic <zpavlinovic@google.com>
Reviewed-by: Julie Qiu <julieqiu@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/cmd/govulncheck/doc.go b/cmd/govulncheck/doc.go
index 387c80d..04f097e 100644
--- a/cmd/govulncheck/doc.go
+++ b/cmd/govulncheck/doc.go
@@ -21,7 +21,7 @@
 WARNING: govulncheck is still EXPERIMENTAL and neither its output or the vulnerability
 database should be relied on to be stable or comprehensive.
 
-# Usage
+Usage
 
 To analyze source code, run govulncheck from the module directory, using the
 same package path syntax that the go command uses:
@@ -52,7 +52,7 @@
 Its output and exit codes are as described above, except that without source it cannot
 produce call stacks.
 
-# Other Modes
+Other Modes
 
 A few flags control govulncheck's output. Regardless of output, govulncheck
 exits with code 0 if there are no vulnerabilities and 3 if there are.
@@ -65,7 +65,7 @@
 The -json flag outputs a JSON object with vulnerability information. The output
 corresponds to the type golang.org/x/vuln/vulncheck.Result.
 
-# Weaknesses
+Weaknesses
 
 Govulncheck uses static analysis, which is inherently imprecise. If govulncheck
 identifies a sequence of calls in your program that leads to a vulnerable