fix: Tweak text as suggested by @richsalz (ietf-tools#4606)

Fixes ietf-tools#4531

Author: larseggert

ietf/templates/nomcom/private_key.html

@@ -7,7 +7,7 @@
     {% origin %}
     <h2>Enter private key</h2>
     <p class="mt-3">
-        In order to access the {{ nomcom.group }} data you have to enter your private key. Please paste it in the text area below. The key must be in the following format:
+        In order to access the {{ nomcom.group }} data you have to enter the NomCom group's private key (which you should have received from the NomCom Chair). The key must be in the following format:
     </p>
     <pre>
   -----BEGIN PRIVATE KEY-----